Semiconductor integrated circuit device and system

ABSTRACT

A semiconductor integrated circuit which can respond to changes of the amount of retained data at the time of standby is provided. The semiconductor integrated circuit comprises a logic circuit (logic) and plural SRAM modules. The plural SRAM modules perform power control independently of the logic circuit, and an independent power control is performed among the plural SRAM modules. Specifically, one terminal and the other terminal of a potential control circuit of each SRAM module are coupled to a cell array and a local power line, respectively. The local power line of one SRAM module and the local power line of the other SRAM module share a shared local power line. A power switch of one SRAM module and a power switch of the other SRAM module are coupled in common to the shared local power line.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2009-211335 filed on Sep. 14, 2009, and the content of which ishereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a semiconductor integrated circuit andan operation method for the same, especially to technology which iseffective in responding to changes of the amount of retained data in astandby state.

BACKGROUND OF THE INVENTION

According to miniaturization in a semiconductor manufacturing process,the number of MOSFETs which are integrated in a single LSI (LSI: LargeScale Integrated circuits) has increased, with an accompanied increaseof leakage current. Especially in the mobile use, under the limitedbattery capacity, a system on a chip (SoC) of this family needs tosatisfy a demand for a strict leakage current. According to Non-patentDocument 1 cited below, the effective method in such a situation iscutting off a power supply to a standby IP, while maintaining a powersupply to a necessary IP. Therefore, the fine grained power gatingsystem which employs many power domains is needed, in order to realize alow power consumption LSI for a mobile SoC.

Patent Document 1 cited below describes an information processing devicein which, in order to manage to balance a low standby current by powergating and a high-speed return from a standby mode by interruption, afirst area comprises a central processing unit and a peripheral circuitmodule and a second area comprises an internal memory and a backupregister, and current supply is controlled by a first power switch inthe first area and current supply is controlled by a second power switchin the second area. When shifting to a standby mode, internalinformation is evacuated to the internal memory or the backup register,then the first power switch is set to an off state to stop currentsupply to the first area, and the second power switch is set to an offstate to maintain the internal information evacuated to the second area.

Patent Document 2 cited below describes that, in order to reduce theleakage current of an SRAM circuit, a switch, a diode coupling MOStransistor, and a resistor are coupled in parallel between a source lineto which a source electrode of a drive MOS transistor is coupled and theground potential line. At the time of standby, the switch coupledbetween the source line and the ground potential line is controlled intoan off state, and the potential of the source line is set to a levelhigher than the ground potential by the relation of the leakage currentof the memory cell, the diode coupling MOS transistor, and the resistor;accordingly, the leakage current is reduced. A switch MOS transistor iscoupled between the ground potential and the ground-potential-side powersource line of the peripheral circuit of SRAM except a word driver. Theswitch MOS transistor is controlled into an off state by a controlsignal at the time of standby. Therefore, the potential of theground-potential-side power source line of the peripheral circuit ofSRAM rises, and the leakage current of the peripheral circuit at thetime of standby is reduced.

Patent Document 3 cited below describes that a leakage current reductioncircuit is coupled between a low potential terminal of a latch circuitor an SRAM cell comprising a CMOS, and a ground potential. The leakagecurrent reduction circuit comprises an NMOS switching transistor, acontrol PMOS transistor, and a control NMOS transistor. Adrain-to-source path of the NMOS switching transistor is coupled betweenthe low potential terminal and the ground potential. A source, a gate,and a drain of the control PMOS transistor are coupled to a power supplyvoltage, a standby signal terminal, and a gate of the NMOS switchingtransistor, respectively. A drain, a gate, and a source of the controlNMOS transistor are coupled to the low potential terminal, a gate of theNMOS switching transistor, and the standby signal terminal,respectively. At the time of operation of the circuit, in response to alow level signal of the standby signal terminal, the control PMOStransistor, the control NMOS transistor, and the NMOS switchingtransistor are set to an on state, an off state, and an on state,respectively, and the low potential terminal is coupled to the groundpotential through a low impedance. Therefore, the latch circuit or SRAMcell comprising a CMOS performs a normal operation. At the time ofstandby, in response to a high level signal of the standby signalterminal, the control PMOS transistor and the control NMOS transistorare set to an off state and an on state, respectively. The NMOSswitching transistor operates like an MOS diode with the leakage currentof the latch circuit or the SRAM cell comprising a CMOS as a biascurrent, thereby keeping the potential of the low potential terminal toa constant potential higher than the ground potential. Accordingly, theleakage current at the time of standby is reduced.

Patent Document 4 cited below describes that, in order to manage tobalance a static noise margin and a write-in margin even at a low powersource voltage in a static type RAM, a voltage supplying circuit iscoupled between a power supply voltage line and a memory cell powersource line. At the time of writing, a high-level control signal issupplied to a gate of a P-channel MOSFET of the voltage supplyingcircuit, and the P-channel MOSFET is set to an off state; accordingly, avoltage of the memory cell power source line is reduced. Therefore, thestatic noise margin is reduced and the write-in margin is improved.

-   (Patent Document 1) Japanese Patent Laid-open No. 2005-011166.-   (Patent Document 2) Japanese Patent Laid-open No. 2004-206745.-   (Patent Document 3) Japanese Patent Laid-open No. 2007-150761.-   (Patent Document 4) Japanese Patent Laid-open No. 2006-085786.-   (Non-patent Document 1) Yusuke Kanno et al, “Hierarchical Power    Distribution With Power Tree in Dozens of Power Domains for 90-nm    Low-Power Multi-CPU SoCs”, IEEE JOURNAL OF SOLID-STATE CIRCUITS,    VOL. 42, NO. 1, JANUARY 2007, PP. 74-83.

SUMMARY OF THE INVENTION

The present inventors were engaged in research and development of asemiconductor integrated circuit with low power consumption in advanceof the present invention.

FIG. 2 illustrates a configuration of a semiconductor integrated circuitexamined by the present inventors in advance of the present invention.

A semiconductor integrated circuit illustrated in FIG. 2 comprises alogic circuit (logic), static type RAMs (SRAM1, SRAM2, SRAM3), and powerswitches PWSW21 and PWSW22. Each of the static type RAMs (SRAM1, SRAM2,SRAM3) comprises a cell array (cell_array), a peripheral circuit(peripheral), a source line potential control circuit (arvss_control),and peripheral circuit power switches PESW21, PESW22 and PESW23.

Since a control signal cnt21 falls at the time of power gating, a powerswitch PWSW21 coupled to the logic circuit (logic) and the static typeRAM (SRAM1) is set to an off state. Therefore, potential of a localpower source vssl21 inside a power source domain rises to a power supplypotential Vdd, and the logic circuit (logic) and the static type RAM(SRAM1) which are coupled to the local power source vssl21 are broughtto a cut-off state. Therefore, all stored data of the static type RAM(SRAM1) coupled to the local power source vssl21 are destroyed.Therefore, data which needs to be saved is stored in other static typeRAMs (SRAM2, SRAM3) coupled to another local power source vssm22, andanother power switch PWSW22 is maintained in an on state also at thetime of power gating. As a result, the another local power source vssm22is maintained at a ground potential Vss.

On the other hand, at the time of power gating, by a control circuit(RSCNT) of the peripheral circuit (peripheral) of the other static typeRAMs (SRAM2, SRAM3) coupled to the other local power source vssm22, theperipheral circuit power switches PESW22 and PESW23 are controlled intoan off state, and the source line potential control circuitarvss_control sets potential of the cell array source lines arvss22,arvss23 of the cell arrays (cell_array) of the other static type RAMs(SRAM2, SRAM3) to a little higher level than the ground potential Vss.Therefore, due to the off state of the peripheral circuit power switchesPESW22, PESW23, it is possible to cut off a leakage current of theperipheral circuits (peripheral) other than a control circuit (RSCNT)and a part of circuits such as a word driver. Furthermore, due to thepotential of a little higher level than the ground potential Vss of thecell array source lines arvss22 and arvss23, it is possible to reducecurrent of the cell array (cell_array) of the other static type RAMs(SRAM2, SRAM3) to such an extent that retained data of the cell array(cell_array) are not destroyed.

FIG. 3 illustrates a configuration of the source line potential controlcircuit (arvss_control) of the other static type RAMs (SRAM2, SRAM3) ofthe semiconductor integrated circuit, illustrated in FIG. 2, examined bythe present inventors in advance of the present invention.

In FIG. 3, the cell array (cell_array) and the source line potentialcontrol circuit (arvss_control) are illustrated, and the peripheralcircuit (peripheral) and the peripheral circuit power switch PESW arealso illustrated. As illustrated in FIG. 3, the source line potentialcontrol circuit (arvss_control) comprises a power switch SW1, a resistorRN1, and a diode coupling MOS transistor MN1, which are coupled inparallel between a cell array source line arvss and the ground potentialVss. In response to falling of a control signal rs, the peripheralcircuit power switch PESW is set to an off state, and a leakage currentof the peripheral circuit (peripheral) other than the control circuit(RSCNT) and a word driver is cut off, and the power switch SW1 of thesource line potential control circuit (arvss_control) is also set to anoff state. As a result, due to a current path through the resistor RN1and the diode coupling MOS transistor MN1 of the source line potentialcontrol circuit (arvss_control), the potential of the cell array sourceline arvss is set to a potential of a little higher level than theground potential Vss, and current of the cell array (cell_array) of theother static type RAM (SRAM23) is reduced to such an extent thatretained data of the cell array (cell_array) are not destroyed.

FIG. 4 illustrates an operating waveform of each part of the source linepotential control circuit (arvss_control) of the other static type RAMs(SRAM2, SRAM3) of the semiconductor integrated circuit illustrated inFIG. 2, examined by the present inventors in advance of the presentinvention.

Since control signals rsb21, rsb22, and rsb23 tall when control signalsrs21, rs22, and rs23 rise, the peripheral circuit power switches PESW21,PESW22, and PESW23 are set to an off state. In this way, by setting theperipheral circuit power switches PESW21, PESW22, and PESW23 to an offstate, a current path from the peripheral circuit (peripheral) of eachof the SRAM modules (SRAM1, SRAM2, SRAM3) to the ground potential Vss iscut off, and the potential of the local power lines vssp21, vssp22, andvssp23 of the peripheral circuit (peripheral) of the SRAM modules(SRAM1, SRAM2, SRAM3) rises to the power supply voltage Vdd or itsneighborhood. However, control circuits (rscnt, RSCNT) which generatecontrol signals rsb21, rsb22, rsb23 for controlling the peripheralcircuit power switches PESW21, PESW22, and PESW23 are coupled not to thelocal power lines vssp21, vssp22, and vssp23, but to the other localpower sources, vssl21, vssm22 directly, because it is necessary tooutput a low-level signal. In addition, a circuit which needs to outputa low-level signal, like a word driver, is coupled to the other localpower sources vssl21 and vssm22 directly, in a similar way. In responseto falling of the control signals rsb21, rsb22, and rsb23, the sourceline potential control circuit (arvss_control) rises voltage of cellarray source lines arvss21, arvss22, and arvss23. However, the voltageis risen to such a level that the retained data of the cell arraycell_array of SRAM1, SRAM2, and SRAM3 are not destroyed (for example,hundreds of mV). Accordingly, it become possible to reduce a leakagecurrent of SRAM1, SRAM2, and SRAM3, while keeping the retained data ofSRAM1, SRAM2, and SRAM3.

Furthermore, when the logic circuit (logic) of a logic circuit part doesnot need to operate, a power supply to the logic circuit (logic) is cutoff, by setting the control signal cnt21 to a low level to bring thepower switch PWSW21 to an off state. As a result, the local power linevssl21 of the logic circuit (logic) goes up to the power supply voltageVdd or its neighborhood. Since the cell array source line arvss21 of thecell array (cell_array) of the static type RAM (SRAM1) coupled to thelocal power line vssl21 goes up to the power supply voltage Vdd or itsneighborhood at this time, the static type RAM (SRAM1) cannot hold theretained data any more.

Furthermore, when a control signal cnt22 is set at a low level in orderto reduce power consumption, a deep standby state is realized. The powerswitch PWSW22 coupled to the other static type RAMs (SRAM2, SRAM3) isset to an off state, and the other local power source vssm22 also goesup to the power supply voltage Vdd or its neighborhood. As a result, itbecomes possible to reduce a leakage current of the other static typeRAMs (SRAM2, SRAM3).

As explained above, it is possible to reduce the consumption current ofa semiconductor integrated circuit which comprises built-in plural SRAMmodules like a system on a chip (SoC), with the control systemillustrated in FIG. 2 through FIG. 4. However, according to the controlsystem illustrated in FIG. 4, the plural SRAM modules are brought to adeep standby state collectively. According to the examination performedby the present inventors, it has been clarified that, in a semiconductorintegrated circuit like a system on a chip (SoC), the amount of retaineddata of plural SRAM modules in a deep standby state changes greatlydepending on an operating state or an operation program. It is alsoclarified by the examination by the present inventors that it isdifficult for the control system illustrated in FIG. 4 to respond tochanges in the amount of retained data in a deep standby state.

The present invention has been made as a result of the examinationdescribed above by the present inventors in advance of the presentinvention.

Therefore, the present invention intends to provide a semiconductorintegrated circuit which can respond to changes in the amount ofretained data in a standby state.

The present invention also intends to reduce a chip area of asemiconductor integrated circuit.

The above and other purposes and new features will become clear fromdescription of the specification and the accompanying drawings of thepresent invention.

The following explains briefly typical inventions to be disclosed by thepresent application.

That is, a typical embodiment of the present invention is asemiconductor integrated circuit comprising a logic circuit (logic) andplural SRAM modules (SRAM2, SRAM3) which can store data related to thelogic circuit.

The plural SRAM modules (SRAM2, SRAM3) can perform power controlindependently of the logic circuit (logic).

An independent power control can be performed among the plural SRAMmodules (SRAM2, SRAM3) (refer to FIG. 5 and FIG. 11).

Specifically, one terminal (arvss) and another terminal (vssm) of apotential control circuit (arvss_control) of each SRAM module of theplural SRAM modules (SRAM2, SRAM3) are coupled to the cell array(cell_array) and a local power line (vssm), respectively.

A local power line (vssm) of one SRAM module of the plural SRAM modules(SRAM2, SRAM3) and a local power line (vssm) of another SRAM module ofthe plural SRAM modules (SRAM2, SRAM3) share a shared local power line(vssm22).

A power switch (PWSW22) of the one SRAM module of the plural SRAMmodules (SRAM2, SRAM3) and a power switch (PWSW23) of the another SRAMmodule of the plural SRAM modules (SRAM2, SRAM3) are coupled in commonto the shared local power line (vssm22) (refer to FIG. 11).

The following explains briefly an effect obtained by the typicalinventions disclosed in the present application.

That is, according to the present invention, it is possible to provide asemiconductor integrated circuit which can respond to changes in theamount of retained data in a standby state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing illustrating an example of a configuration of asemiconductor integrated circuit according to Embodiment 24 of thepresent invention which comprises three built-in SRAM modules (SRAM1,SRAM2, SRAM3) according to one of Embodiment 1 through Embodiment 23 ofthe present invention;

FIG. 2 is a drawing illustrating a configuration of a semiconductorintegrated circuit examined by the present inventors in advance of thepresent invention;

FIG. 3 is a drawing illustrating a configuration of a source linepotential control circuit (arvss_control) of other static type RAMs(SRAM2, SRAM3) of the semiconductor integrated circuit, illustrated inFIG. 2, examined by the present inventors in advance of the presentinvention;

FIG. 4 is a drawing illustrating an operating waveform of each part ofthe source line potential control circuit (arvss_control) of the otherstatic type RAMs (SRAM2, SRAM3) of the semiconductor integrated circuit,illustrated in FIG. 2, examined by the present inventors in advance ofthe present invention;

FIG. 5 is a drawing illustrating a configuration of a semiconductorintegrated circuit according to Embodiment 1 of the present invention;

FIG. 6 is a drawing illustrating a configuration of a source linepotential control circuit (arvss_control) of each of SRAM modules(SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuit accordingto Embodiment 1 of the present invention illustrated in FIG. 5;

FIG. 7 is a drawing illustrating a configuration of three SRAM modules(SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuit accordingto Embodiment 1 of the present invention illustrated in FIG. 5;

FIG. 8 is a drawing illustrating a configuration of a source linepotential control circuit (arvss_control) of the SRAM module of thesemiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 7;

FIG. 9 is a drawing illustrating another configuration of three SRAMmodules (SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.5;

FIG. 10 is a drawing illustrating a configuration of a chip layout ofthree SRAM modules (SRAM1, SRAM2, SRAM3) of the semiconductor integratedcircuit according to Embodiment 1 of the present invention illustratedin FIG. 5;

FIG. 11 is a drawing illustrating a configuration of a semiconductorintegrated circuit according to Embodiment 2 of the present invention;

FIG. 12 is a drawing illustrating a configuration of plural memory cells(MC) included in each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment 1of the present invention illustrated in FIG. 5 or the semiconductorintegrated circuit according to Embodiment 2 of the present inventionillustrated in FIG. 11;

FIG. 13 is a drawing illustrating another configuration of the pluralmemory cells (MC) included in each SRAM module of three SRAM modules(SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuit accordingto Embodiment 1 of the present invention illustrated in FIG. 5 or thesemiconductor integrated circuit according to Embodiment 2 of thepresent invention illustrated in FIG. 11;

FIG. 14 is a drawing illustrating a configuration of a semiconductorintegrated circuit according to Embodiment 3 of the present invention;

FIG. 15 is a drawing illustrating a configuration of plural memory cells(MC) included in each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment 3of the present invention illustrated in FIG. 14;

FIG. 16 is a drawing illustrating another configuration of plural memorycells (MC) included in each SRAM module of three SRAM modules (SRAM1,SRAM2, SRAM3) of the semiconductor integrated circuit according toEmbodiment 3 of the present invention illustrated in FIG. 14;

FIG. 17 is a drawing illustrating yet another configuration of pluralmemory cells (MC) included in each SRAM module of three SRAM modules(SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuit accordingto Embodiment 3 of the present invention illustrated in FIG. 14;

FIG. 18 is a drawing illustrating a configuration of a semiconductorintegrated circuit according to Embodiment 4 of the present invention;

FIG. 19 is a drawing illustrating a configuration of a semiconductorintegrated circuit according to Embodiment 5 of the present invention;

FIG. 20 is a drawing illustrating a configuration of a semiconductorintegrated circuit according to Embodiment 6 of the present invention;

FIG. 21 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 7 of the present invention;

FIG. 22 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 8 of the present invention;

FIG. 23 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 9 of the present invention;

FIG. 24 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 10 of the present invention;

FIG. 25 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 11 of the present invention;

FIG. 26 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 12 of the present invention;

FIG. 27 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 13 of the present invention;

FIG. 28 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 14 of the present invention;

FIG. 29 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 15 of the present invention;

FIG. 30 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 16 of the present invention;

FIG. 31 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 17 of the present invention;

FIG. 32 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 18 of the present invention;

FIG. 33 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 19 of the present invention;

FIG. 34 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 20 of the present invention;

FIG. 35 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 21 of the present invention;

FIG. 36 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 22 of the present invention;and

FIG. 37 is a drawing illustrating a configuration of each SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) included in a semiconductorintegrated circuit according to Embodiment 23 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. Summary of thePreferred Embodiments

First, a summary is explained about typical embodiments of the inventiondisclosed in the present application. A reference symbol in parenthesesreferring to a component of the drawing in the summary explanation aboutthe typical embodiments only illustrates what is included in the conceptof the component to which the reference symbol is attached.

(1) A typical embodiment of the present invention is a semiconductorintegrated circuit comprising a logic circuit (logic) and plural SRAMmodules (SRAM2, SRAM3) which can store data related to the logiccircuit.

The plural SRAM modules (SRAM2, SRAM3) can perform power controlindependently of the logic circuit (logic).

An independent power control can be performed among the plural SRAMmodules (SRAM2, SRAM3) (refer to FIG. 5 and FIG. 11).

According to the embodiment, it is possible to respond to changes in theamount of retained data in a standby state.

A semiconductor integrated circuit according to a preferred embodimentfurther comprises another SRAM modules (SRAM1) which can perform powercontrol in common with the logic circuit (logic).

The logic circuit and the another SRAM module can be controlled incommon to a power gating state.

Before the logic circuit (logic) and the another SRAM module (SRAM1) arecontrolled in common to the power gating state, data of the another SRAMmodule (SRAM1) can be evacuated to at least one SRAM module of theplural SRAM modules (SRAM2, SRAM3) (refer to FIG. 5 and FIG. 11).

A semiconductor integrated circuit according to another preferredembodiment comprises plural power switches (PWSW21, PWSW22, PWSW23).

Each SRAM module of the another SRAM module (SRAM1) and the plural SRAMmodules (SRAM2, SRANM3) is coupled with each power switch of the pluralpower switches (PWSW21, PWSW22, PWSW23) in series.

The each SRAM module can be controlled to the power gating state, bycontrolling the each power switch of the plural power switches (PWSW21,PWSW22, PWSW23) to an off state.

The each SRAM module is controlled to an active state and a standbystate, by controlling the each power switch of the plural power switches(PWSW21, PWSW22, PWSW23) to an on state (refer to FIG. 5 and FIG. 11).

According to a more preferred embodiment, the each SRAM module comprisesa peripheral circuit (peripheral), a cell array (cell_array), and apotential control circuit (arvss_control).

In the each SRAM module, the cell array (cell_array) and the potentialcontrol circuit (arvss_control) are coupled in series, and the seriescoupling of the cell array (cell_array) and the potential controlcircuit (arvss_control) is coupled with the peripheral circuit(peripheral) in parallel.

According to another more preferred embodiment, in the each SRAM modulecontrolled to the active state, an inter-terminal voltage (arvss-vssm)between one terminal (arvss) and another terminal (vssm) of thepotential control circuit (arvss_control) is controlled to a state of alow voltage, a power supply voltage (Vdd-Vss) is supplied to theperipheral circuit (peripheral), and the power supply voltage (Vdd-Vss)is supplied to the cell array (cell_array) by the potential controlcircuit (arvss_control).

In the each SRAM module controlled to the standby state, theinter-terminal voltage (arvss-vssm) of the potential control circuit(arvss_control) is controlled to a state of voltage higher than the lowvoltage, the power supply voltage (Vdd-Vss) to the peripheral circuit(peripheral) is cut off, and an operating voltage lower than the powersupply voltage (Vdd-Vss) is supplied to the cell array (cell_array) bythe potential control circuit (arvss_control).

In a specific embodiment, one terminal (arvss) and another terminal(vssm) of the potential control circuit (arvss_control) of each of theSRAM modules are coupled to the cell array (cell_array) and a localpower line (vssm), respectively.

A local power line (vssm) of one SRAM module of the plural SRAM modules(SRAM2, SRAM3) and a local power line (vssm) of another SRAM module ofthe plural SRAM modules (SRAM2, SRAM3) share a shared local power line(vssm22).

A power switch (PWSW22) of the one SRAM module of the plural SRAMmodules (SRAM2, SRAM3), and a power switch (PWSW23) of the another SRAMmodule of the plural SRAM modules (SRAM2, SRAM3) are coupled in commonto the shared local power line (vssm22) (refer to FIG. 11).

In a more specific embodiment, a P-well which is used for formation ofplural N-channel MOS transistors of the cell array (cell_array) of theone SRAM module of the plural SRAM modules (SRAM2, SRAM3) and a P-wellwhich is used for formation of plural N-channel MOS transistors of thecell array (cell_array) of the another SRAM module of the plural SRAMmodules (SRAM2, SRAM3) are formed by a common P-well (refer to FIG. 11).

In another more specific embodiment, between the one terminal (arvss)and the another terminal (vssm) of the potential control circuit(arvss_control) of the each SRAM module, a voltage drop element (RN1,MN1) which changes the inter-terminal voltage (arvss-vssm) to the highvoltage state and a control switch (SW1) which changes theinter-terminal voltage (arvss-vssm) to the low voltage state are coupled(refer to FIG. 3).

In a different more specific embodiment, the cell array (cell_array) ofthe each SRAM module comprises plural SRAM memory cells (MC) comprisingone pair of drive N-channel MOS transistors (MNDL, MNDR), and one pairof load P-channel MOS transistors (MPUL, MPUR), and one pair of transferN-channel MOS transistors (MNSL, MNSR) (refer to FIG. 12).

A semiconductor integrated circuit according to the most specificembodiment comprises plural data processing units (CPU1, CPU2, Video,Audio).

Each data processing unit of the plural data processing units comprisesthe logic circuit (logic) and the plural SRAM modules (SRAM2, SRAM3)(refer to FIG. 1).

(2) A typical embodiment of another viewpoint of the present inventionis an operation method of a semiconductor integrated circuit comprisinga logic circuit (logic) and plural SRAM modules (SRAM2, SRAM3) which canstore data related to the logic circuit. The operation method concernedcomprises the following steps (refer to FIG. 5 and FIG. 11).

That is a step of performing a power control for the logic circuit(logic) independently of the plural SRAM modules (SRAM2, SRAM3).

That is a step of performing an independent power control among theplural SRAM modules(SRAM2, SRAM3).

According to the embodiment, it is possible to respond to changes in theamount of retained data in a standby state.

2. Further Detailed Description of the Preferred Embodiments

Next, embodiments are explained further in full detail. In the entiredrawings for explaining the preferred embodiments of the presentinvention, the same symbol is attached to a component which has the samefunction, and the repeated explanation thereof is omitted.

Embodiment 1

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 1>>

FIG. 5 illustrates a configuration of a semiconductor integrated circuitaccording to Embodiment 1 of the present invention.

A semiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5 is different from thesemiconductor integrated circuit illustrated in FIG. 2, examined by thepresent inventors in advance of the present invention, in the followingpoints.

That is, in the semiconductor integrated circuit according to Embodiment1 of the present invention illustrated in FIG. 5, a power switch PWSW22is coupled between a local power source vssm22 of an SRAM module (SRAM2)and a ground potential Vss, a control signal cnt22 is supplied to acontrol gate of the power switch PWSW22; a power switch PWSW23 iscoupled between a local power source vssm23 of an SRAM module (SRAM3)and the ground potential Vss, and a control signal cnt23 is supplied toa control gate of the power switch PWSW23.

Inside the SRAM module (SRAM2) of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.5, a peripheral circuit power switch PEWS22 is coupled between aperipheral circuit (peripheral) and the local power source vssm22, and asource line potential control circuit (arvss_control) is coupled betweena cell array (cell_array) and the local power source vssm22. A controlsignal rsb22 of a control circuit (RSCNT) of the peripheral circuit(peripheral) is supplied to a control gate of the peripheral circuitpower switch PEWS22, and to a control input terminal of the source linepotential control circuit (arvss_control).

Inside the SRAM module (SRAM3) of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.5, a peripheral circuit power switch PEWS23 is coupled between aperipheral circuit (peripheral) and the local power source vssm23, and asource line potential control circuit (arvss_control) is coupled betweena cell array (cell_array) and the local power source vssm23. A controlsignal rsb23 of a control circuit (RSCNT) of a peripheral circuit(peripheral) is supplied to a control gate of the peripheral circuitpower switch PEWS23, and to a control input terminal of a source linepotential control circuit (arvss_control).

Inside the SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.5, as is the case with the SRAM module (SRAM1) of the semiconductorintegrated circuit illustrated in FIG. 2, a peripheral circuit powerswitch PEWS21 is coupled between a peripheral circuit (peripheral) andthe local power source vssl21, and a source line potential controlcircuit (arvss_control) is coupled between a cell array (cell_array) andthe local power source vssl21. A control signal rsb21 of a controlcircuit (RSCNT) of the peripheral circuit (peripheral) is supplied to acontrol gate of the peripheral circuit power switch PEWS21, and to acontrol input terminal of the source line potential control circuit(arvss_control).

The local power source vssl21 of the SRAM module (SRAM1) of thesemiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5 is coupled to a power switchPWSW21 and a logic circuit (logic), as is the case with the SRAM module(SRAM1) of the semiconductor integrated circuit illustrated in FIG. 2.

FIG. 6 illustrates a configuration of the source line potential controlcircuit (arvss_control) of the SRAM module (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5.

In FIG. 6, the cell array (cell_array), the source line potentialcontrol circuit (arvss_control), and the power switch PWSW areillustrated. As illustrated in FIG. 6, the source line potential controlcircuit (arvss_control) comprises a power switch NSW, a resistor RESI,and a diode coupling MOS transistor DIOD, which are coupled in parallelbetween a cell array source line arvss and a local power source vssm.

<<Active State>>

When executing write operation or read operation to one SRAM module ofthree SRAM modules (SRAM1, SRAM2, SRAM3) in the semiconductor integratedcircuit according to Embodiment 1 of the present invention illustratedin FIG. 5, one of three control signals rsb21, rsb22, and rsb23 is setat a high level, and at the same time, one of three control signalscnt21, cnt22, and cnt23 is set at a high level.

In an SRAM module which is brought to an active state, the power switchPWSW is set to an on state by the control signal cnt, and, in responseto rising of the control signal rsb of the control circuit (RSCNT) ofthe peripheral circuit (peripheral), the peripheral circuit power switchPESW is set to an on state, and the peripheral circuit (peripheral) isactivated. The power switch NSW of the source line potential controlcircuit (arvss_control) is also set to an on state. Accordingly, by thesource line potential control circuit (arvss_control), the potential ofthe cell array source line arvss is set to the ground potential Vss;therefore, it becomes possible to execute the write operation or theread operation to the cell array (cell_array) of the SRAM module whichis brought to an active state.

<<Deep Standby State>>

In the semiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5, when the control signal cnt21is set at a low level, the power switch PWSW21 is set to an off state.Therefore, the logic circuit (logic) and the SRAM module (SRAM1) arebrought to a deep standby state. When data of the SRAM module (SRAM1)needs to be saved, the data of the SRAM module (SRAM1) is evacuated toother SRAM modules (SRAM2, SRAM3) before the SRAM module (SRAM1) isbrought to the deep standby state. When the control signal cnt22 is setat a low level, the power switch PWSW22 is set to an off state;accordingly, the SRAM module (SRAM2) is brought to a deep standby state.When data of the SRAM module (SRAM2) needs to be saved, the data of theSRAM module (SRAM2) is evacuated to other SRAM modules (SRAM1, SRAM3)before the SRAM module (SRAM2) is brought to the deep standby state.Similarly, when the control signal cnt23 is set at a low level, thepower switch PWSW23 is set to an off state; accordingly, the SRAM module(SRAM3) is brought to a deep standby state. When data of the SRAM module(SRAM3) needs to be saved, the data of the SRAM module (SRAM3) isevacuated to other SRAM modules (SRAM1, SRAM2) before the SRAM module(SRAM3) is brought to the deep standby state. In this way, according tothe semiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5, it is possible to change theamount of retained data in a deep standby state.

<<Standby State>>

In the semiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5, when three control signalscnt21, cnt22, and cnt23 are set at a high level and one of three controlsignals rsb21, rsb22, and rsb23 is set at a low level, one of three SRAMmodules (SRAM1, SRAM2, SRAM3) is brought to a standby state. In an SRAMmodule which is brought to a standby state, in response to falling ofthe control signal rsb of the control circuit (RSCNT) of the peripheralcircuit (peripheral), the peripheral circuit power switch PESW is set toan off state, and a leakage current of the peripheral circuits(peripheral) other than the control circuit (RSCNT) is cut off. Thepower switch NSW of the source line potential control circuit(arvss_control) is also set to an off state. Therefore, due to a currentpath through the resistor RESI and the diode coupling MOS transistorDIOD of the source line potential control circuit (arvss_control), thepotential of the cell array source line arvss is set at a potential of alittle higher level than the ground potential Vss, and current of thecell array (cell_array) of the SRAM module in the standby state isreduced to such an extent that retained data of the cell array(cell_array) are not destroyed.

<<A Configuration of the SRAM Module>>

FIG. 7 illustrates a configuration of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment 1of the present invention illustrated in FIG. 5.

The SRAM module illustrated in FIG. 7 comprises, in addition to cellarrays (ARRAY_BIT[1], - - - , ARRAY_BIT[n]) and source line potentialcontrol circuits (ARVSS_CNT[1], - - - , ARVSS_CNT[n]), a control unit(CONTROL) comprising a control circuit, a word driver (WORD_DRIVER)which drives a word line, I/O units (IO[1], - - - , IO[n]) which outputand input data, and power switches (PWSW[1], - - - , PWSW[n]).

The cell arrays (ARRAY_BIT[1], - - - , ARRAY_BIT[n]) comprise pluralmemory cells (MC) coupled to plural word lines wl[1], - - - , wl[m], andplural complementary bit-line pairs bb[1], bt[1], bb[2], and bt[2]. Theword driver (WORD_DRIVER) comprises plural CMOS inverters coupled to theplural word lines wl[1], - - - , wl[m]. The I/O units (IO[1], - - - ,IO[n]) comprise plural selectors (SELECTOR) coupled to the pluralcomplementary bit-line pairs bb[1], bt[1], bb[2], and bt[2], and pluralsense amplifiers (SA). Each of the source line potential controlcircuits (ARVSS_CNT[1], - - - , ARVSS_CNT[n]) comprises a power switchNSW and a resistor RESI and a diode coupling MOS transistor DIOD whichare coupled in parallel between a cell array source line arvss and alocal power source vssm, as is the case with FIG. 6. The control unit(CONTROL) comprises a decoder (DECODER) which drives the plural CMOSinverters of the word driver (WORD_DRIVER) and the plural selectors(SELECTOR) of the I/O units (IO[1], - - - , IO[n]), in response toaddress signals a[1], - - - , a[k]. The control unit (CONTROL) comprisesa CMOS inverter which generates a control signal rsb1 to be supplied toa control gate of the power switch NSW of the source line potentialcontrol circuits (ARVSS_CNT[1], - - - , ARVSS_CNT[n]), and a CMOSinverter which generates a control signal cnt to be supplied to acontrol gate of the power switches (PWSW[1], - - - , PWSW[n]).

In a semiconductor integrated circuit like a system on a chip (SoC), inorder to satisfy a user's various demands, a compiled RAM (CRAM) inwhich various combination of element components of SRAM is possible isemployed. In the compiled RAM (CRAM) illustrated in FIG. 7, the sourceline potential control circuits (ARVSS_CNT[1], - - - , ARVSS_CNT[n]) andthe power switches (PWSW[1], - - - , PWSW[n]) are arranged in units ofbit([1], - - - , [n]). Accordingly, in the compiled RAM (CRAM)illustrated in FIG. 7, it becomes possible to respond easily a user'sdemand, by changing the number of columns of the memory cell (MC) andthe number of the I/O units (IO[1], - - - , IO[n]), depending on thenumber of bits which satisfies the user's demand. Namely, in thecompiled RAM (CRAM) of FIG. 7, the source line potential controlcircuits (ARVSS_CNT[1], - - - , ARVSS_CNT[n]) and the power switches(PWSW[1], - - - , PWSW[n]) are arranged in units of bit([1], - - - ,[n]); therefore, even when the number of bit of the compiled RAM (CRAM)changes, the number of the source line potential control circuits andthe number of the power switches are increased or decreased, byresponding automatically to the change in the number of total memorycells. Therefore, it is possible to keep appropriately the potential ofthe cell array source line arvss.

The compiled RAM (CRAM) illustrated in FIG. 7 adopts a two-columnmultiplex system in which one I/O line (q[1], - - - , q[n]) is shared bytwo memory cell columns. Naturally, the number of column multiplexes canbe set as an arbitrary number.

FIG. 8 illustrates a configuration of the source line potential controlcircuit (arvss_control) of the SRAM module of the semiconductorintegrated circuit according to Embodiment 1 of the present inventionillustrated in FIG. 7.

The source line potential control circuit (arvss_control) illustrated inFIG. 8 comprises a resistor RESI, an NMOS switching transistor MDIOD_SW,a control PMOS transistor MPG, and a control NMOS transistor MNG. Theresistor RESI and the NMOS switching transistor MDIOD_SW are coupledbetween the cell array source line arvss and the local power sourcevssm. A drain-to-source path of the NMOS switching transistor MDIOD_SWis coupled between the cell array source line arvss and the local powersource vssm. A source, a gate, and a drain of the control PMOStransistor MPG are coupled to a power supply voltage gcnt, a standbysignal terminal rs, and a gate of the NMOS switching transistorMDIOD_SW, respectively. A drain, a source, and a gate of the controlNMOS transistor MNG are coupled to the cell array source line arvss, agate of the NMOS switching transistor MDIOD_SW, and the standby signalterminal rs, respectively. At the time of operation of the circuit,responding to a low-level signal of the standby signal terminal rs, thecontrol PMOS transistor MPG, the control NMOS transistor MNG, and theNMOS switching transistor MDIOD_SW are set to an on state, an off state,and an on state, respectively, and the cell array source line arvss iscoupled to the local power source vssm through low impedance;accordingly, the cell array (cell_array) performs the normal operation.At the time of standby, responding to a high-level signal of the standbysignal terminal rs, the control PMOS transistor MPG and the control NMOStransistor MNG are set to an off state and an on state, respectively.The NMOS switching transistor MDIOD_SW operates like an MOS diode with aleakage current of the cell array (cell_array) serving as a biascurrent. Accordingly, the potential of the cell array source line arvssis held to a constant potential higher than the local power source vssm,thereby reducing the leakage current at the time of standby.

FIG. 9 is a drawing illustrating another configuration of the SRAMmodules (SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.5.

An SRAM module illustrated in FIG. 9 is different from the SRAM moduleillustrated in FIG. 7 in the point that the source line potentialcontrol circuit (arvss_control) of the SRAM module illustrated in FIG. 9adopts the circuit configuration of FIG. 8 instead of the circuitconfiguration of FIG. 6. In the SRAM module illustrated in FIG. 9, onecontrol PMOS transistor MPG and one control NMOS transistor MNG whichdrive plural NMOS switching transistors MDIOD_SW in plural source linepotential control circuits (arvss_control) are arranged at one placeinside the control unit (CONTROL).

As described above, according to the semiconductor integrated circuitaccording to Embodiment 1 of the present invention explained withreference to FIG. 5 through FIG. 9, when the first power switch PWSW21coupled to the first SRAM module (SRAM1) is controlled to an off stateby the first control signal cnt21 at a low level, the first local powerline vssl21 is set at a high level; accordingly, the logic circuit(logic) and the first SRAM module (SRAM1) are brought to a deep standbystate. In the present state, when the second power switch PWSW22 coupledto the second SRAM module (SRAM2) is controlled to an on state by thesecond control signal cnt22 at a high level, the second local power linevssm22 is set at a low level; accordingly, the second SRAM module(SRAM2) is brought to an active state or a standby state by the controlsignal rsb22. Also in the present state, when the third power switchPWSW23 coupled to the third SRAM module (SRAM3) is controlled to an onstate by the third control signal cnt23 at a high level, the third localpower line vssm23 is set at a low level; accordingly, the third SRAMmodule (SRAM3) is brought to an active state or a standby state by thecontrol signal rsb23. Therefore, according to the semiconductorintegrated circuit according to Embodiment 1 of the present inventionexplained with reference to FIG. 5 through FIG. 9, it becomes possibleto respond to changes in the amount of retained data of SRAM in a deepstandby state.

In the semiconductor integrated circuit according to Embodiment 1 of thepresent invention explained in FIG. 5 through FIG. 9, it is possible toreplace N-channel MOS transistors serving as the power switches PWSW21,PWSW22, and PWSW23 with P-channel MOS transistors and to change thecoupling point of the power switches PWSW21, PWSW22, and PWSW23 from theside of the ground potential Vss to the side of the power supply voltageVdd. In the case, the local power lines vssl21, vssm22, and vssm23 arealso changed from the side of the ground potential Vss to the localpower lines vddl21, vddm22, and vddm23 on the side of the power supplyvoltage Vdd. Furthermore, N-channel MOS transistors serving as theperipheral circuit power switches PESW21, PESW22, and PESW23 are alsoreplaced with P-channel MOS transistors, and the coupling point of theperipheral circuit power switches PESW21, PESW22, and PESW23 is alsochanged to between the local power lines vddl21, vddm22, and vddm23 onthe side of the power supply voltage Vdd and the peripheral circuit(peripheral). The coupling point of the source line potential controlcircuit (arvss_control) is also changed to between the local power linesvddl21, vddm22, and vddm23 on the side of the power supply voltage Vddand the cell array (cell_array).

However, in the semiconductor integrated circuit according to Embodiment1 of the present invention explained in FIG. 5 through FIG. 9, it isnecessary that the first power switch PWSW21 is exclusively employed forthe first SRAM module (SRAM1), the second power switch PWSW22 isexclusively employed for the second SRAM module (SRAM2), and the thirdpower switch PWSW23 is exclusively employed for the third SRAM module(SRAM3), and that the first local power line vssl21, the second localpower line vssm22, and the third local power line vssm23 areelectrically separated from each other. Since each power switch of threepower switches PWSW21, PWSW22, and PWSW23 is exclusively employed toeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3), an elementsize of each power switch needs to be set up corresponding to theoperating current of each SRAM module. Since the first local power linevssl21, the second local power line vssm22, and the third local powerline vssm23 need to be electrically separated from each other, each of Pwell regions which are used for formation of plural N-channel MOStransistors of each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) needs to be electrically separated from each other.

<<A Chip Layout of Embodiment 1>>

FIG. 10 illustrates a configuration of a chip layout of three SRAMmodules (SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.5.

As illustrated in FIG. 10, the first local power line vssl21 for thelogic circuit (logic) and the first SRAM module (SRAM1), the secondlocal power line vssm22 for the second SRAM module (SRAM2), and thethird local power line vssm23 for the third SRAM module (SRAM3) areelectrically separated from each other. The first power switch PWSW21employed exclusively for the first SRAN module (SRAM1) and the logiccircuit (logic) is coupled between the first local power line vssl21 andthe ground potential Vss. The second power switch PWSW22 employedexclusively for the second SRAM module (SRAM2) is coupled between thesecond local power line vssm22 and the ground potential Vss. The thirdpower switch PWSW23 employed exclusively for the third SRAM module(SRAM3) is coupled between the third local power line vssm23 and theground potential Vss.

Plural N-channel MOS transistors for the first power switch PWSW21 areformed in a first power switch area PWSW_AREA1, plural N-channel MOStransistors for the second power switch PWSW22 are formed in a secondpower switch area PWSW_AREA2, and plural N-channel MOS transistors forthe third power switch PWSW23 are formed in a third power switch areaPWSW_AREA3.

The logic circuit (logic) and the plural N-channel MOS transistors ofthe first SRAM module (SRAM1) coupled to the first local power linevssl21 are formed in a first P-well region WELL_AREA1, the pluralN-channel MOS transistors of the second SRAM module (SRAM2) coupled tothe second local power line vssm22 are formed in a second P-well regionWELL_AREA2, and the plural N-channel MOS transistors of the third SRAMmodule (SRAM3) coupled to the third local power line vssm23 are formedin a third P-well region WELL_AREA3. As illustrated in FIG. 10, on themain surface of a semiconductor chip of the semiconductor integratedcircuit, it is necessary to electrically separate the first P-wellregion WELL_AREA1 and the second P-well region WELL_AREA2 by an N typearea which has the minimum separation space wspace. It is necessary toelectrically separate the second P-well region WELL_AREA2 and the thirdP-well region WELL_AREA3 by an N type area which has the minimumseparation space wspace. Therefore, the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.10 has a drawback that the semiconductor chip area becomes comparativelylarge.

The above is about a case of a semiconductor integrated circuit oftriple well structure. In the case of a semiconductor integrated circuitof double well structure, an N-well region of a power gating area wherecutting-off by a power switch is different from the side of the powersupply voltage Vdd needs to be separated by a P-well region. Therefore,also in the semiconductor integrated circuit of double well structure,there is a drawback that the semiconductor chip area becomescomparatively large, as is the case with the triple well structure.

A semiconductor integrated circuit according to Embodiment 2 of thepresent invention explained below will remove the present drawback.

Embodiment 2

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 2>>

FIG. 11 illustrates a configuration of a semiconductor integratedcircuit according to Embodiment 2 of the present invention.

A semiconductor integrated circuit according to Embodiment 2 of thepresent invention illustrated in FIG. 11 is different from thesemiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5 in the following points.

That is, in the semiconductor integrated circuit according to Embodiment2 of the present invention illustrated in FIG. 11, a local power line ofthe second SRAM module (SRAM2) and a local power line of the third SRAMmodule (SRAM3) share the second local power line vssm22. Furthermore,the second power switch PWSW22 and the third power switch PWSW23 whichare coupled between the shared second local power line vssm22 and theground potential Vss are shared by the second SRAM module (SRAM2) andthe third SRAM module (SRAM3).

Also in the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, a local power line ofthe logic circuit (logic) and a local power line of the first SRAMmodule (SRAM1) share a first local power line vssl21. Furthermore, thefirst power switch PWSW21 coupled between the shared first local powerline vssl21 and the ground potential Vss is shared by the logic circuit(logic) and the first SRAM module (SRAM1).

In the first SRAM module (SRAM1), a peripheral circuit power switchPESW21 is coupled between a peripheral circuit (peripheral) and thefirst local power line vssl21, and a source line potential controlcircuit, which comprises an active power switch SW21, a resistor RN21, adiode coupling MOS transistor MN21, and a switch MSW21, is coupledbetween a cell array source line arvss21 of a cell array (cell_array)and the first local power line vssl21. A parallel coupling body of theresistor RN21 and the diode coupling MOS transistor MN21 are coupled tothe switch MSW21 in series, and the switch MSW21 and the first powerswitch PWSW21 are coupled in series.

Also in the second SRAM module (SRAM2), a peripheral circuit powerswitch PESW22 is coupled between a peripheral circuit (peripheral) andthe second local power line vssm22, and a source line potential controlcircuit, which comprises an active power switch SW22, a resistor RN22, adiode coupling MOS transistor MN22, and a switch MSW22, is coupledbetween a cell array source line arvss22 of a cell array (cell_array)and the second local power line vssm22. A parallel coupling body of theresistor RN22 and the diode coupling MOS transistor MN22 are coupled tothe switch MSW22 in series, and the switch MSW22 and the second powerswitch PWSW22 are coupled in series.

Also in the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between a peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit, which comprises an active power switch SW23, a resistor RN23, adiode coupling MOS transistor MN23, and a switch MSW23, is coupledbetween a cell array source line arvss23 of a cell array (cell_array)and the second local power line vssm22. A parallel coupling body of theresistor RN23 and the diode coupling MOS transistor MN23 are coupled tothe switch MSW23 in series, and the switch MSW23 and the third powerswitch PWSW23 are coupled in series.

Since it suffices that the switches MSW21, MSW22, and MSW23 of thesource line potential control circuit flow a small leakage current atthe time of standby, it is possible to make the size of the switchessmall, to suppress an overhead of the semiconductor chip occupied area.

<<Active State of the Logic and the First SRAM>>

When a control signal cnt21 is set at a high level in order to bring thelogic circuit (logic) and the first SRAM module (SRAM1) into an activestate, the first power switch PWSW21 is set to an on state, and thepotential of the first local power line vssl21 to which a logic circuit(logic) and the first SRAM module (SRAM1) are coupled is set at theground potential Vss. Furthermore, a control signal rsb21 is set at ahigh level, and the peripheral circuit power switch PESW21 and theactive power switch SW21 are set to an on state; accordingly, aperipheral circuit (peripheral) and a cell array (cell_array) of thefirst SRAM module (SRAM1) are brought to an active state. Therefore, inthe present active state, it is possible for the logic circuit (logic)to perform logic operation, and it is also possible to execute writeoperation or read operation of the first SRAM module (SRAM1).

<<Standby State of the Logic and the First SRAM>>

When the control signal cnt21 is set at a high level in order to bringthe logic circuit (logic) and the first SRAM module (SRAM1) into astandby state, the first power switch PWSW21 is set to an on state, andthe potential of the first local power line vssl21 to which the logiccircuit (logic) and the first SRAM module (SRAM1) are coupled is set atthe ground potential Vss. The control signal rsb21 is set at a low leveland the peripheral circuit power switch PESW21 and the active powerswitch SW21 are set to an off state. Furthermore, a control signal rs21is set at a high level and the switch MSW21 of the source line potentialcontrol circuit is set to an on state. Therefore, the potential of thecell array source line arvss21 of the cell array (cell_array) of thefirst SRAM module (SRAM1) is set at a level a little higher than theground potential Vss. Accordingly, it becomes possible to reduce currentof the cell array (cell_array) to such an extent that the retained dataof the cell array (cell_array) are not destroyed.

<<Array Cut-Off State of the Logic and the First SRAM>>

When the control signal cnt21 is set at a low level in order to bringthe logic circuit (logic) and the first SRAM module (SRAM1) into anarray cut-off state, the first power switch PWSW21 is set to an offstate, and the potential of the first local power line vssl21 to whichthe logic circuit (logic) and the first SRAM module (SRAM1) are coupledis set at a level approximately near the power supply voltage Vdd, andthe control signal rsb21 is set at a low level and the peripheralcircuit power switch PESW21 and the active power switch SW21 are set toan off state. Furthermore, the control signal rs21 is set at a lowlevel, and the switch MSW21 of the source line potential control circuitis set to an off state.

<<Active State of the Second and the Third SRAM>>

When control signals cnt22 and cnt23 are set at a high level in order tobring the second and the third SRAM module (SRAM2, SRAM3) into an activestate, the second, the third power switch PWSW22 and PWSW23 are set toan on state. Therefore, the potential of the second local power linevssm22 to which the second and the third SRAM module (SRAM2, SRAM3) arecoupled is set at the ground potential Vss. Furthermore, At least one ofthe control signals rsb22 and rsb23 is set at a high level, and at leastone of the peripheral circuit power switches PESW22 and PESW23 and atleast one of the active power switches SW22 and SW23 are set to an onstate. Accordingly, the peripheral circuit (peripheral) and the cellarray (cell_array) of at least one of the second and the third SRAMmodule (SRAM2, SRAM3) are set to an active state. Therefore, it becomespossible to execute write operation or read operation to the SRAM modulein the active state.

<<Standby State of One of the Second and the Third SRAM>>

When the control signals cnt22 and cnt23 are set at a high level inorder to bring one of the second and the third SRAM module (SRAM2,SRAM3) into a standby state, the second and the third power switchPWSW22 and PWSW23 are set to an on state. Accordingly, the potential ofthe second local power line vssm22 to which the second and the thirdSRAM module (SRAM2, SRAM3) are coupled is set at the ground potentialVss. Furthermore, one of the control signals rsb22 and rsb23 is set at alow level, and one of the peripheral circuit power switches PESW22 andPESW23 and one of the active power switches SW22 and SW23 are set to anoff state. Furthermore, one of the control signals rs22 and rs23 is setat a high level, and one of the switches MSW22 and MSW23 of the sourceline potential control circuit is set to an on state. Therefore, thepotential of one of the cell array source lines arvss22 and arvss23 ofthe cell array (cell_array) of one of the second and the third SRAMmodule (SRAM2, SRAM3) is set at a level a little higher than the groundpotential Vss; accordingly, It becomes possible to reduce current of thecell array (cell_array) to such an extent that the retained data of thecell array (cell_array) are not destroyed. In the standby state of oneof the second and the third SRAM module, to an SRAM module in an activestate, the control signals rs22 and rs23 may be set at either a highlevel or a low level without problems.

<<Array Cut-Off State of One of the Second and the Third SRAM>>

One of the control signals cnt22 and cnt23 is set at a low level inorder to cut off one array of the second and the third SRAM module(SRAM2, SRAM3). Furthermore, one of or both of the control signals rsb22and rsb23 are set at a low level, and one of or both of the peripheralcircuit power switches PESW22 and PESW23 and one of or both of theactive power switches SW22 and SW23 are set to an off state.Furthermore, only one of the control signals rs22 and rs23 is set at alow level, and only one of the switches MSW22 and MSW23 of the sourceline potential control circuit is set to an off state. An SRAM modulefor which array cut-off is not performed may be set either in a standbystate or in an active state, without problems.

<<Array Cut-Off State of Both the Second and the Third SRAM>>

When both control signals rsb22 and rsb23 are set at a low level, inorder to bring both the second and the third SRAM module (SRAM2, SRAM3)into an array cut-off state, both peripheral circuit power switchesPESW22 and PESW23 and both active power switches SW22 and SW23 are setto an off state. Furthermore, both control signals rs22 and rs23 are setat a low level, and both deep standby switches MSW22 and MSW23 of thesource line potential control circuit are set to an off state.

<<A Deep Standby State of the Second and the Third SRAM>>

When both control signals cnt22 and cnt23 are set at a low level, boththe second and the third power switch PWSW22 and PWSW23 are set to anoff state. Accordingly, the potential of the second local power linevssm22 to which the second and the third SRAM module (SRAM2, SRAM3) arecoupled is set at a level near the power supply voltage Vdd, due to aleakage current of the second and the third SRAM module.

<<A Chip Layout of Embodiment 2>>

As described above, when practicing the chip layout of three SRAMmodules (SRAM1, SRAM2, and SRAM3) of the semiconductor integratedcircuit according to Embodiment 2 of the present invention illustratedin FIG. 11, it becomes possible to omit an N type area which has theminimum separation space wspace between the second P-well regionWELL_AREA2 and the third P-well region WELL_AREA3 as illustrated in thelayout pattern of FIG. 10. The reason is as follows. In thesemiconductor integrated circuit according to Embodiment 2 of thepresent invention illustrated in FIG. 11, the local power line of thesecond SRAM module (SRAM2) and the local power line of the third SRAMmodule (SRAM3) share the second local power line vssm22, therefore it isnot necessary to electrically separate the second P-well regionWELL_AREA2 and the third P-well region WELL_AREA3. As a result,according to the semiconductor integrated circuit according toEmbodiment 2 of the present invention illustrated in FIG. 11, it becomespossible to remove the drawback that the semiconductor chip area becomescomparatively large in the semiconductor integrated circuit according toEmbodiment 1 of the present invention illustrated in FIG. 10.

Furthermore, according to the semiconductor integrated circuit accordingto Embodiment 2 of the present invention illustrated in FIG. 11, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3). Therefore, each element size of the secondpower switch PWSW22 and the third power switch PWSW23 does not need tobe set up corresponding to each operating current of the second SRAMmodule (SRAM2) and the third SRAM module (SRAM3). As a result, it ispossible to reduce each element size of the second power switch PWSW22and the third power switch PWSW23 in the semiconductor integratedcircuit according to Embodiment 2 of the present invention illustratedin FIG. 11, compared with the semiconductor integrated circuit accordingto Embodiment 1 of the present invention illustrated in FIG. 5.

Furthermore, in the semiconductor integrated circuit according toEmbodiment 2 of the present invention illustrated in FIG. 11, the onresistance of the switches MSW21, MSW22, and MSW23 can be madecomparatively large in value, therefore, it is not necessary to enlargespecially the element size of these switches MSW21, MSW22, and MSW23.Therefore, increase of the semiconductor chip area of the semiconductorintegrated circuit according to Embodiment 2 of the present inventionillustrated in FIG. 11 due to the addition of the switches MSW21, MSW22,and MSW23 is negligible small. In the case of the semiconductorintegrated circuit of double well structure explained in the lastportion of Embodiment 1, an effect of reduction of the semiconductorchip area is the same.

<<Memory Cell>>

FIG. 12 illustrates a configuration of plural memory cells (MC) includedin each SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 1 of thepresent invention illustrated in FIG. 5 or the semiconductor integratedcircuit according to Embodiment 2 of the present invention illustratedin FIG. 11.

As illustrated in FIG. 12, each of plural memory cells (MC) comprisesone pair of drive N-channel MOS transistors (MNDL, MNDR), one pair ofload P-channel MOS transistors (MPUL, MPUR), and one pair of transferN-channel MOS transistors (MNSL, MNSR). A gate and a P-well of one pairof transfer N-channel MOS transistors (MNSL, MNSR) are coupled to a wordline wl and a local power source vssm, respectively. A source and aP-well of one pair of drive N-channel MOS transistors (MNDL, MNDR) arecoupled to a cell array source line arvss and the local power sourcevssm, respectively. A source and an N-well of one pair of load P-channelMOS transistors (MPUL, MPUR) are coupled to the power supply voltageVdd.

A drain of the left-hand side drive N-channel MOS transistor (MNDL), adrain of the left-hand side load P-channel MOS transistor (MPUL), a gateof the right-hand side drive N-channel MOS transistor (MNDR), and a gateof the right-hand side load P-channel MOS transistor (MPUR) form onememory node of the memory cell (MC). The one memory node of the memorycell (MC) is coupled to a noninverting bit line bt via a source-to-drainpath of the left-hand side transfer N-channel MOS transistor (MNSL).

A drain of the right-hand side drive N-channel MOS transistor (MNDR), adrain of the right-hand side load P-channel MOS transistor (MPUR), agate of the left-hand side drive N-channel MOS transistor (MNDL), and agate of the left-hand side load P-channel MOS transistor (MPUL) form theother memory node of the memory cell (MC). The other memory node of thememory cell (MC) is coupled to a noninverting bit line bb via asource-to-drain path of the right-hand side transfer N-channel MOStransistor (MNSR).

FIG. 13 illustrates another configuration of the plural memory cells(MC) included in each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment 1of the present invention illustrated in FIG. 5 or the semiconductorintegrated circuit according to Embodiment 2 of the present inventionillustrated in FIG. 11.

The memory cell (MC) illustrated in FIG. 13 is different from the memorycell (MC) illustrated in FIG. 12 in the point that, in the memory cell(MC) illustrated in FIG. 13, a P-well of one pair of drive N-channel MOStransistors (MNDL, MNDR) and a P-well of one pair of transfer N-channelMOS transistors (MNSL, MNSR) are not coupled to the local power sourcevssm like the memory cell (MC) of FIG. 12, but coupled to the cell arraysource line arvss. That is, depending on magnitude of a leakagecomponent of the memory cell (MC), the memory cell (MC) illustrated inFIG. 13 exhibits greater reduction effect of the leakage current thanthe memory cell (MC) illustrated in FIG. 12. Specifically, when asubstrate leakage is more dominant than a subthreshold leakage, thememory cell (MC) of FIG. 13 exhibits greater reduction effect of theleakage current.

Embodiment 3

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 3>>

FIG. 14 illustrates a configuration of a semiconductor integratedcircuit according to Embodiment 3 of the present invention.

A semiconductor integrated circuit according to Embodiment 3 of thepresent invention illustrated in FIG. 14 is different from thesemiconductor integrated circuit according to Embodiment 2 of thepresent invention illustrated in FIG. 11 in the following points.

The first difference is that the switches MSW21, MSW22, and MSW23, eachcomprising the N-channel MOS transistor of the source line potentialcontrol circuit of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 2 of thepresent invention illustrated in FIG. 11, are replaced by switchesMPSW21, MPSW22, and MPSW23, each comprising a P-channel MOS transistorof a source line potential control circuit of the semiconductorintegrated circuit according to Embodiment 3 of the present inventionillustrated in FIG. 14.

The next difference is that the coupling point of each of the switchesMPSW21, MPSW22, and MPSW23 of the source line potential control circuitof three SRAM modules (SRAM1, SRAM2, SRAM3) of the semiconductorintegrated circuit according to Embodiment 3 of the present inventionillustrated in FIG. 14 is changed from between the cell array(cell_array) and the local power lines vssl21 and vssm22, to between thecell array (cell_array) and the power supply voltage Vdd.

An operating current of a memory cell (MC) in read operation isdominated by a current which flows from a bit line to the cell arraysource line arvss on the side of the ground potential Vss, an operatingcurrent of a memory cell (MC) in write operation is dominated by acurrent which flows in driving a bit line, and a current which flowsinto the cell array source line arvdd on the side of the power supplyvoltage Vdd is very small. Consequently, it suffices that the switchesMPSW21, MPSW22, and MPSW23 of the source line potential control circuitallow a small leakage current to pass at the time of standby; therefore,it is possible to make the size of the switches small, and to suppressan overhead of the semiconductor chip occupied area.

<<An Active State of the Logic and the First SRAM>>

When the control signal cnt21 is set at a high level in order to bringthe logic circuit (logic) and the first SRAM module (SRAM1) into anactive state, the first power switch PWSW21 is set to an on state, andthe potential of the first local power line vssl21 to which the logiccircuit (logic) and the first SRAM module (SRAM1) are coupled is set atthe ground potential Vss. Furthermore, the control signal rsb21 is setat a high level, the control signal rsp21 is set at a low level, and theperipheral circuit power switch PESW21, the active power switch SW21,and the switch MPSW21 are set to an on state. Accordingly, theperipheral circuit (peripheral) and the cell array (cell_array) of thefirst SRAM module (SRAM1) are brought to an active state. Therefore, inthe present active state, it is possible for the logic circuit (logic)to perform logic operation, and it is also possible to execute writeoperation or read operation of the first SRAM module (SRAM1).

When executing write operation of the first SRAM module (SRAM1), it ispossible to perform a write assist which weakens retaining function ofold data of the cell array (cell_array) of the first SRAM module(SRAM1), by changing the control signal rsp21 toward the high-leveldirection and reducing the degree of conduction of the switch MPSW21.

<<A Standby State of the Logic and the First SRAM>>

When the control signal cnt21 is set at a high level in order to bringthe logic circuit (logic) and the first SRAM module (SRAM1) into astandby state, the first power switch PWSW21 is set to an on state.Therefore, the potential of the first local power line vssl21 to whichthe logic circuit (logic) and the first SRAM module (SRAM1) are coupledis set at the ground potential Vss. The control signal rsb21 is set at alow level and the peripheral circuit power switch PESW21 and the activepower switch SW21 are set to an off state. Furthermore, the controlsignal rsp21 is set at a low level, and the switch MPSW21 of the sourceline potential control circuit is set to an on state. Therefore, thepotential of one cell array source line arvss21 of the cell array(cell_array) of the first SRAM module (SRAM1) is set at a level a littlehigher than the ground potential Vss; accordingly, current of the cellarray (cell_array) is reduced to such an extent that retained data ofthe cell array are not destroyed.

<<A Deep Standby State of the Logic and the First SRAM>>

When the control signal cnt21 is set at a low level in order to bringthe logic circuit (logic) and the first SRAM module (SRAM1) into a deepstandby state, the first power switch PWSW21 is set to an off state;accordingly, the potential of the first local power line vssl21 to whichthe logic circuit (logic) and the first SRAM module (SRAM1) are coupledis set at a level near the power supply voltage Vdd. Therefore, it ispossible to reduce a leakage current of the memory cell (MC) of the cellarray (cell_array) of the first SRAM module (SRAM1) to almost zero.

<<An Active State of One of the Second and the Third SRAM>>

When one of the control signals cnt22 and cnt23 is set at a high levelin order to bring one of the second and the third SRAM module (SRAM2,SRAM3) into an active state, one of the second and the third powerswitch PWSW22 and PWSW23 is set to an on state. Therefore, the potentialof the second local power line vssm22 to which the second and the thirdSRAM module (SRAM2, SRAM3) are coupled is set at the ground potentialVss. Furthermore, one of the control signals rsb22 and rsb23 is set at ahigh level, one of the control signals rsp22 and rsp23 is set at a lowlevel, and one of the peripheral circuit power switches PESW22 andPESW23, one of the active power switches SW22 and SW23, and one of thedeep standby switches MPSW22 and MPSW23 are set to an on state.Accordingly, the peripheral circuit (peripheral) and the cell array(cell_array) of one of the second and the third SRAM modules (SRAM 2,SRAM3) are set to an active state. Therefore, it becomes possible toexecute write operation or read operation to the SRAM module in theactive state. When executing write operation to the SRAM module in thepresent active state, as is the case with the first SRAM module (SRAM1),it is possible to perform a write assist which weakens retainingfunction of old data of a cell array of the SRAM module in an activestate, by changing one of the control signals rsp22 and rsp23 toward thehigh-level direction and reducing the degree of conduction of one of theswitches MPSW22 and MPSW23.

<<Standby State of One of the Second and the Third SRAM>>

When one of the control signals cnt22 and cnt23 is set at a high levelin order to bring one of the second and the third SRAM module (SRAM2,SRAM3) into a standby state, one of the second and the third powerswitch PWSW22 and PWSW23 is set to an on state. Therefore, the potentialof the second local power line vssm22 to which the second and the thirdSRAM module (SRAM2, SRAM3) are coupled is set at the ground potentialVss. Furthermore, one of the control signals rsb22 and rsb23 is set at alow level, and one of the peripheral circuit power switches PESW22 andPESW23 and one of the active power switches SW22 and SW23 are set to anoff state. Furthermore, the control signals rsp22 and rsp23 are set at alow level, and the switches MPSW22 and MPSW23 of the source linepotential control circuit are set to an on state.

Therefore, the potential of the cell array source lines arvss22 andarvss23 of the cell array (cell_array) of one of the second and thethird SRAM module (SRAM2, SRAM3) is set at a level a little higher thanthe ground potential Vss; accordingly, it becomes possible to reducecurrent of the cell array (cell_array) to such an extent that theretained data of the cell array (cell_array) are not destroyed.

<<Array Power Cut-Off State of Only One of the Second and the ThirdSRAM>>

When one of the control signals cnt22 and cnt23 is set at a high levelin order to bring only one of the second and the third SRAM module(SRAM2, SRAM3) into an array power cut-off state, only one of the secondand the third power switch PWSW22 and PWSW23 is set to an on state.Therefore, the potential of the second local power line vssm22 to whichthe second and the third SRAM module (SRAM2, SRAM3) are coupled is setat the ground potential Vss. Furthermore, only one of the controlsignals rsb22 and rsb23 is set at a low level, and only one of theperipheral circuit power switches PESW22 and PESW23 and only one of theactive power switches SW22 and SW23 are set to an off state.Furthermore, only one of the control signals rsp22 and rsp23 is set at ahigh level, and only one of the switches MPSW22 and MPSW23 of the sourceline potential control circuit is set to an off state.

In one of the SRAM modules in which the switch MPSW22 or the switchMPSW23 is set to an off state, it is possible to reduce effectively aleakage current of a memory cell (MC) which is brought to an array powercut-off state, compared with a standby state in which data is held.

<<An Array Power Cut-Off State of Both the Second and the Third SRAM>>

When one of the control signals cnt22 and cnt23 is set at a high level,only one of the second and the third power switch PWSW22 and PWSW23 isset to an on state. Accordingly, the potential of the second local powerline vssm22 to which the second and the third SRAM module (SRAM2, SRAM3)are coupled is set at the ground potential Vss. Furthermore, bothcontrol signals rsb22 and rsb23 are set at a low level, and bothperipheral circuit power switches PESW22 and PESW23 and both activepower switches SW22 and SW23 are set to an off state. Furthermore, bothcontrol signals rsp22 and rsp23 are set at a high level, and bothswitches MPSW22 and MPSW23 of the source line potential control circuitare set to an off state. Compared with a standby state in which data isheld, it is possible to reduce effectively a leakage current of thememory cell (MC) of both the second and the third SRAM in an array powercut-off state. When compared with an array power gating in which thesecond and the third power switch PWSW22 and PWSW23 are controlled to anoff state with the use of the control signals cnt22 and cnt23 set at alow level, the present array power cut-off state exhibits an effect thata high-speed return from the cut-off state becomes possible.

<<A Deep Standby State of Both the Second and the Third SRAM>>

When the control signal cnt22 is set at a low level in order to bringboth the second and the third SRAM module (SRAM2, SRAM3) into a deepstandby state, the power switch PWSW22 is set to an off state.Accordingly, the potential of the second local power line vssm22 towhich the second and the third SRAM module (SRAM2, SRAM3) are coupled isset at a level near the power supply voltage Vdd, and it is possible toreduce a leakage current to almost zero.

<<Memory Cell>>

FIG. 15 illustrates a configuration of plural memory cells (MC) includedin each SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 3 of thepresent invention illustrated in FIG. 14.

The memory cell (MC) illustrated in FIG. 15 is different from the memorycell (MC) illustrated in FIG. 12 in the point that a source of one pairof load P-channel MOS transistors (MPUL, MPUR) is coupled not to thepower supply voltage Vdd, but to the cell array source line arvdd towhich the deep standby switch MPSW is coupled.

FIG. 16 illustrates another configuration of plural memory cells (MC)included in each SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3)of the semiconductor integrated circuit according to Embodiment 3 of thepresent invention illustrated in FIG. 14.

The memory cell (MC) illustrated in FIG. 16 is different from the memorycell (MC) illustrated in FIG. 15 in the point that, an N-well of onepair of load P-channel MOS transistors (MPUL, MPUR) is coupled not tothe power supply voltage Vdd, but to the cell array source line arvdd towhich the deep standby switch MPSW is coupled.

The memory cell (MC) illustrated in FIG. 16 is more advantageous thanthe memory cell (MC) illustrated in FIG. 15 in a viewpoint of reductionof a leakage current of the memory cell (MC). However, in the memorycell (MC) illustrated in FIG. 16, it is necessary to separateelectrically an N-well of one pair of load P-channel MOS transistors(MPUL, MPUR) coupled to the cell array source line arvdd, from an N-wellof the peripheral circuit (peripheral) coupled to the power supplyvoltage Vdd, or other P-channel MOS transistors (MPUL, MPUR) except forthe SRAM module.

For example, in a semiconductor integrated circuit of triple wellstructure, in order to separate electrically plural N-wells of pluralP-channel MOS transistors mutually, it is necessary to form pluralN-wells spaced out mutually on a P-type substrate. Therefore, the memorycell (MC) illustrated in FIG. 15 is more advantageous than the memorycell (MC) illustrated in FIG. 16 in a viewpoint of reduction of a chiparea of a semiconductor integrated circuit. As a result, in designing asemiconductor integrated circuit, if priority is given to reduction of achip area of a semiconductor integrated circuit, the memory cell (MC)illustrated in FIG. 15 will be chosen, and if priority is given toreduction of a leakage current of a memory cell (MC), the memory cell(MC) illustrated in FIG. 16 will be chosen.

FIG. 17 illustrates yet another configuration of plural memory cells(MC) included in each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment 3of the present invention illustrated in FIG. 14.

The memory cell (MC) illustrated in FIG. 17 is different from the memorycell (MC) illustrated in FIG. 15 in the point that a PMOS substrate biasvoltage Vbp is supplied to an N-well of one pair of load P-channel MOStransistors (MPUL, MPUR), and that an NMOS substrate bias voltage Vbn issupplied to a P-well of one pair of drive N-channel MOS transistors(MNDL, MNDR) and one pair of transfer N-channel MOS transistors (MNSL,MNSR). The PMOS substrate bias voltage Vbp and the NMOS substrate biasvoltage Vbn are generated by a substrate bias generation circuit (notshown). The substrate bias generation circuit generates the PMOSsubstrate bias voltage Vbp and the NMOS substrate bias voltage Vbn whichhave suitable voltage values, responding to change of a manufacturingprocess, temperature, or a power supply voltage. Therefore, a logicthreshold voltage of a CMOS inverter, which comprises one pair of loadP-channel MOS transistors (MPUL, MPUR) and one pair of drive N-channelMOS transistors (MNDL, MNDR) of a memory cell (MC), is set at a voltagevalue of approximately middle of the operating voltage arvdd−arvss. As aresult, a leakage current of the memory cell (MC) is reduced and it ispossible to improve the data retaining characteristics of the memorycell (MC).

Embodiment 4

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 4>>

FIG. 18 illustrates a configuration of a semiconductor integratedcircuit according to Embodiment 4 of the present invention.

A semiconductor integrated circuit according to Embodiment 4 of thepresent invention illustrated in FIG. 18 is different from thesemiconductor integrated circuit according to Embodiment 3 of thepresent invention illustrated in FIG. 14 in the following points.

That is, in the semiconductor integrated circuit according to Embodiment4 of the present invention illustrated in FIG. 18, the deep standbyswitches MSWS21, MSWS22, and MSWS23 comprising the N-channel MOStransistors in the semiconductor integrated circuit according toEmbodiment 2 of the present invention illustrated in FIG. 11 are addedbetween the cell array source lines arvss21, arvss22, and arvss23 andthe local power lines vssl21 and vssm22.

As a result, in the semiconductor integrated circuit according toEmbodiment 4 of the present invention illustrated in FIG. 18, the deepstandby switches MPSWS21, MPSWS22, and MPSWS23 comprising P-channel MOStransistors are coupled between the power supply voltage Vdd and thecell array source line arvdd21, arvdd22 and arvdd23 of the cell array(cell_array), and the deep standby switches MSWS21, MSWS22, and MSWS23comprising N-channel MOS transistors are coupled between the cell arraysource lines arvss21, arvss22, and arvss23 and the local power linevssl21 and vssm22.

In a deep standby state of the logic circuit (logic) and the first SRAMmodule (SRAM1), the control signal cnt21 is set at a low level, thefirst power switch PWSW21 is set to an off state, the control signalrsb21 is set at a low level, and the peripheral circuit power switchPESW21 and the active power switch SW21 are set to an off state.Furthermore, the control signal rs21 is set at a low level, the controlsignal rsp21 is set at a high level, and the switches MSW21 and MPSW21of the source line potential control circuit are set to an off state.

In a deep standby state of the second SRAM module (SRAM2), the controlsignal cnt22 is set at a low level and the second power switch PWSW22 isset to an off state, and the control signal rsb22 is set at a low leveland the peripheral circuit power switch PESW22 and the active powerswitch SW22 are set to an off state. Furthermore, the control signalrs22 is set at a low level and the control signal rsp22 is set at a highlevel, and the switches MSW22 and MPSW22 of the source line potentialcontrol circuit are set to an off state.

Furthermore, in a deep standby state of the third SRAM module (SRAM3),the control signal cnt23 is set at a low level and the third powerswitch PWSW23 is set to an off state, and the control signal rsb23 isset at a low level and the peripheral circuit power switch PESW23 andthe active power switch SW23 are set to an off state. Furthermore, thecontrol signal rs23 is set at a low level and the control signal rsp23is set at a high level, and the switches MSW23 and MPSW23 of the sourceline potential control circuit are set to an off state.

In the semiconductor integrated circuit according to Embodiment 4 of thepresent invention illustrated in FIG. 18, to three SRAM modules (SRAM1,SRAM2, SRAM3), the deep standby switches MPSWS21, MPSWS22, and MPSWS23,each comprising a P-channel MOS transistor on the power supply side, andthe deep standby switches MSWS21, MSWS22, and MSWS23, each comprising anN-channel MOS transistor on the ground side, are coupled. Especially, ina deep standby state, the power-supply-side deep standby switchesMPSWS21, MPSWS22, and MPSWS23 and the ground-side deep standby switchesMSWS21, MSWS22, and MSWS23 are both controlled into an off state;accordingly, it is possible to reduce reliably a leakage current of thecell array (cell_array) which is controlled into a deep standby state.Therefore, in plural memory cells (MC) of a cell array (cell_array),even in the state where the power supply voltage Vdd is supplied to anN-well of one pair of load P-channel MOS transistors (MPUL, MPUR), andthe potential of the local power line vssm22 is supplied to a P-well ofone pair of drive N-channel MOS transistors (MNDL, MNDR) and one pair oftransfer N-channel MOS transistors (MNSL, MNSR), it becomes possible toreduce a leakage current of the memory cell (MC) in a deep standbystate. The leakage current in a deep standby state is given by a weakreverse current of a PN junction between the N-well to which the powersupply voltage Vdd is supplied and the P-well to which the potential ofthe local power line vssm22 is supplied.

Embodiment 5

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 5>>

FIG. 19 illustrates a configuration of a semiconductor integratedcircuit according to Embodiment 5 of the present invention.

A semiconductor integrated circuit according to Embodiment 5 of thepresent invention illustrated in FIG. 19 is different from thesemiconductor integrated circuit according to Embodiment 2 of thepresent invention illustrated in FIG. 11 in the following points.

That is, in the semiconductor integrated circuit according to Embodiment5 of the present invention illustrated in FIG. 19, a drain-to-sourcepath of P-channel MOS transistors MCP21, MCP22, and MCP23 is coupledbetween a gate of the N-channel MOS transistors MN21, MN22, and MN23 ofthe source line potential control circuit of three SRAM modules (SRAM1,SRAM2, SRAM3) and the cell array source lines arvss21, arvss22, andarvss23, and a drain-to-source path of N-channel MOS transistors MCN21,MCN22, and MCN23 is coupled between a gate of the N-channel MOStransistors MN21, MN22, and MN23 of the source line potential controlcircuit of three SRAM modules (SRAM1, SRAM2, SRAM3) and the local powerlines vssl21 and vssm22.

First, in an active state of the SRAM modules (SRAM1, SRAM2, SRAM3), thecontrol signals cnt21, cnt22, and cnt23 are set at a high level, and thepower switches PWSW21, PWSW22, and PWSW23 are set to an on state, andthe local power lines vssl21 and vssm22 are set at the ground potentialVss. Next, the control signals rsb21, rsb22, and rsb23 are set at a highlevel, and the peripheral circuit power switches PESW21, PESW22, andPESW23, and the active power switches SW21, SW22, and SW23 are set to anon state. Accordingly, the peripheral circuit (peripheral) and the cellarray (cell_array) of the SRAM modules (SRAM1, SRAM2, SRAM3) are set toan active state.

Next, in a standby state of the SRAM modules (SRAM1, SRAM2, SRAM3), thecontrol signal cnt21, cnt22, and cnt23 are set at a high level, and thepower switches PWSW21, PWSW22, and PWSW23 are set to an on state. Thecontrol signals rsb21, rsb22, and rsb23 are set at a low level, and theperipheral circuit power switches PESW21, PESW22, and PESW23, and theactive power switches SW21, SW22, and SW23 are set to an off state. Atthis time, the control signals rs21, rs22, and rs23 are set at a lowlevel, and the P-channel MOS transistors MCP21, MCP22, and MCP23 are setto an on state; accordingly, the N-channel MOS transistors MN21, MN22,and MN23 of the source line potential control circuit operate as adiode. Therefore, the potential of the cell array source line arvss21,arvss22, and arvss23 of the cell array (cell_array) of the SRAM modules(SRAM1, SRAM2, SRAM3) is set at a level a little higher than the groundpotential Vss. Accordingly, current of the cell array (cell_array) isreduced to such an extent that retained data of the cell array are notdestroyed.

In a deep standby state of the SRAM modules (SRAM1, SRAM2, SRAM3), thecontrol signals cnt21, cnt22, and cnt23 are set at a low level, and thepower switches PWSW21, PWSW22, and PWSW23 are set to an off state. Thecontrol signals rsb21, rsb22, and rsb23 are set at a low level, and theperipheral circuit power switch PESW21, PESW22, and PESW23, and theactive power switch SW21, SW22, and SW23 are set to an off state. Atthis time, the control signals rs21, rs22, and rs23 are set at a highlevel, the N-channel MOS transistors MCN21, MCN22, and MCN23 are set toan on state, and the N-channel MOS transistors MN21, MN22, and MN23 ofthe source line potential control circuit are set to an off state.Therefore, it is possible to reduce greatly the operating current of thecell array (cell_array) of the SRAM modules (SRAM1, SRAM2, SRAM3), bysetting high a value of resistance of the resistor RN21, RN22, and RN23of the source line potential control circuit.

Embodiment 6

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 6>>

FIG. 20 illustrates a configuration of a semiconductor integratedcircuit according to Embodiment 6 of the present invention.

A semiconductor integrated circuit according to Embodiment 6 of thepresent invention illustrated in FIG. 20 is different from thesemiconductor integrated circuit according to Embodiment 5 of thepresent invention illustrated in FIG. 19 in the following points.

That is, the resistors RN21, RN22, and RN23 of the source line potentialcontrol circuit of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 5 of thepresent invention illustrated in FIG. 19 are replaced by N-channel MOStransistors MRN21, MRN22, and MRN23 of the source line potential controlcircuit of three SRAM modules (SRAM1, SRAM2, SRAM3) of the semiconductorintegrated circuit according to Embodiment 6 of the present inventionillustrated in FIG. 20. Since a CMOS inverter is coupled to a controlgate of each of the N-channel MOS transistors MRN21, MRN22, and MRN23,inverted signals of the control signals rs21, rs22, and rs23 aresupplied to the control gates of the N-channel MOS transistors MRN21,MRN22, and MRN23, respectively.

Therefore, in a deep standby state of the semiconductor integratedcircuit according to Embodiment 6 of the present invention illustratedin FIG. 20, when the N-channel MOS transistors MN21, MN22, and MN23 ofthe source line potential control circuit are set to an off state by thecontrol signals rs21, rs22, and rs23 of a high level, the N-channel MOStransistors MRN21, MRN22, and MRN23 are set to an off state;accordingly, it is possible to reduce greatly the operating current ofthe cell array (cell_array) of the SRAM modules (SRAM1, SRAM2, SRAM3).

Embodiment 7

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 7>>

FIG. 21 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 7 of the present invention.

In a semiconductor integrated circuit according to Embodiment 7 of thepresent invention, although not illustrated in FIG. 21 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 7 of the present invention, a peripheral circuitpower switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22.

<<Source Line Potential Control Circuit>>

As illustrated in FIG. 21, the source line potential control circuit ofeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 7 of thepresent invention comprises a resistor RN1 and an N-channel MOStransistor MN_L1 coupled in parallel between the cell array source linearvss and the local power line vssm.

A source-to-drain path of two P-channel MOS transistors MP_L1 and MP_L2is coupled in series between the power supply voltage Vdd and a controlgate of the N-channel MOS transistor MN_L1, and a drain-to-source pathof two N-channel MOS transistors MN_L5 and MN_L4 is coupled in seriesbetween a drain and the control gate of the N-channel MOS transistorMN_L1.

A drain-to-source path of an N-channel MOS transistor MN_L3 is coupledbetween the control gate of the N-channel MOS transistor MN_L1 and thelocal power line vssm, and the control signal rs2 is supplied to acontrol gate of the N-channel MOS transistor MN_L3.

The control signal rsb1 is supplied to an input terminal of the CMOSinverter INV_L1, and an output signal of the CMOS inverter INV_L1 issupplied to a control gate of the P-channel MOS transistor MP_L2 and acontrol gate of the N-channel MOS transistor MN_L4. The control signalrs2 is supplied to a control gate of the P-channel MOS transistor MP_L1and an input terminal of the CMOS inverter INV_L2, and an output signalof the CMOS inverter INV_L2 is supplied to a control gate of theN-channel MOS transistor MN_L5.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 21, thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set at a high level, a high level, and a low level, respectively.Therefore, the power switch PWSW is set to an on state, two P-channelMOS transistors MP_L1 and MP_L2 which are coupled in series are set toan on state, and the N-channel MOS transistor MN_L1 is set to an onstate.

Therefore, the local power line vssm is set at the ground potential Vssand the peripheral circuit power switch PESW is set to an on state;accordingly, the peripheral circuit (peripheral) is set to an activestate. Furthermore, the potential of the cell array source line arvss isset at the ground potential Vss due to the on state of the N-channel MOStransistor MN_L1, and the cell array (cell_array) is also set to anactive state; accordingly, it becomes possible to execute writeoperation or read operation of the SRAM module illustrated in FIG. 21.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 21, thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set at a high level, a low level, and a low level, respectively.Therefore, the power switch PWSW is set to an on state, and twoN-channel MOS transistors MN_L5 and MN_L 4 which are coupled in seriesare set to an on state; accordingly, the N-channel MOS transistor MN_L1operates as a diode.

Therefore, the peripheral circuit power switch PESW is set to an offstate, and the peripheral circuit (peripheral) is set to a standbystate. Furthermore, The potential of the cell array source line arvss isset at a level a little higher than the ground potential Vss due to thediode operation of the N-channel MOS transistor MN_L1, and the currentof the cell array is reduced to such an extent that retained data of thecell array (cell_array) are not destroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 21, thecontrol signal rsb1 and the control signal rs2 are set at a low leveland a high level, respectively. Therefore, the N-channel MOS transistorMN_L3 is set to an on state, and the N-channel MOS transistor MN_L1 isset to an off state. Therefore, it is possible to reduce greatly theoperating current of the cell array (cell_array) of the SRAM module, bysetting high a value of resistance of the resistor RN1 of the sourceline potential control circuit.

Embodiment 8

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 8>>

FIG. 22 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 8 of the present invention.

In a semiconductor integrated circuit according to Embodiment 8 of thepresent invention, although not illustrated in FIG. 22 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 8 of the present invention, a peripheral circuitpower switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22.

<<Source Line Potential Control Circuit>>

As illustrated in FIG. 22, the source line potential control circuit ofeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 8 of thepresent invention comprises a resistor RN1 and an N-channel MOStransistor MN_L1 coupled in parallel between the cell array source linearvss and the local power line vssm.

A source-to-drain path of two P-channel MOS transistors MP_L1 and MP_L2is coupled in series between the power supply voltage Vdd and a controlgate of the N-channel MOS transistor MN_L1, and a source-to-drain pathof two P-channel MOS transistors MP_L5 and MP_L4 is coupled in seriesbetween a drain and the control gate of the N-channel MOS transistorMN_L1.

A drain-to-source path of a N-channel MOS transistor MN_L3 is coupledbetween the control gate of the N-channel MOS transistor MN_L1 and thelocal power line vssm, and the control signal rs2 is supplied to acontrol gate of the N-channel MOS transistor MN_L3.

The control signal rsb1 is supplied to a control gate of the P-channelMOS transistor MP_L4 and an input terminal of the CMOS inverter INV_L1,and an output signal of the CMOS inverter INV_L1 is supplied to acontrol gate of the P-channel MOS transistor MP_L2. The control signalrs2 is supplied to a control gate of the P-channel MOS transistor MP_L1and a control gate of the P-channel MOS transistor MP_L5.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 22, thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set at a high level, a high level, and a low level, respectively.Accordingly, the power switch PWSW is set to an on state, two P-channelMOS transistors MP_L1 and MP_L2 which are coupled in series are set toan on state, and the N-channel MOS transistor MN_L1 is set to an onstate.

Therefore, the local power line vssm is set at the ground potential Vssand the peripheral circuit power switch PESW is set to an on state;accordingly, the peripheral circuit (peripheral) is set to an activestate. Furthermore, the potential of the cell array source line arvss isset at the ground potential Vss due to the on state of the N-channel MOStransistor MN_L1, and the cell array (cell_array) is also set to anactive state; accordingly, it becomes possible to execute writeoperation or read operation of the SRAM module illustrated in FIG. 22.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 22, thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set at a high level, a low level, and a low level, respectively.Accordingly, the power switch PWSW is set to an on state, two P-channelMOS transistors MP_L5 and MP_L4 which are coupled in series are set toan on state, and the N-channel MOS transistor MN_L1 operates as a diode.

Therefore, the peripheral circuit power switch PESW is set to an offstate, and the peripheral circuit (peripheral) is set in a standbystate. Furthermore, the potential of the cell array source line arvss isset at a level a little higher than the ground potential Vss due to thediode operation of the N-channel MOS transistor MN_L1, and current ofthe cell array (cell_array) is reduced to such an extent that retaineddata of the cell array are not destroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 22, thecontrol signal rsb1 and the control signal rs2 are set at a low leveland a high level, respectively. Therefore, the N-channel MOS transistorMN_L3 is set to an on state, and the N-channel MOS transistor MN_L1 isset to an off state. Therefore, it is possible to reduce greatly theoperating current of the cell array (cell_array) of the SRAM module, bysetting high a value of resistance of the resistor RN1 of the sourceline potential control circuit.

Embodiment 9

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 9>>

FIG. 23 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 9 of the present invention.

In a semiconductor integrated circuit according to Embodiment 9 of thepresent invention, although not illustrated in FIG. 23 but as is thecase with the semiconductor integrated circuit according to Embodiment 3of the present invention illustrated in FIG. 14, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

Furthermore, In the semiconductor integrated circuit according toEmbodiment 9 of the present invention, although not illustrated in FIG.23 but as is the case with the semiconductor integrated circuitaccording to Embodiment 3 of the present invention illustrated in FIG.14, the deep standby switches MPSWS21, MPSWS22, and MPSWS23 comprising aP-channel MOS transistor are coupled between the power supply voltageVdd and the cell array source lines arvdd21, arvdd22, and arvdd23 of thecell array (cell_array).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 9 of the present invention, a peripheral circuitpower switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22.

<<A Source Line Potential Control Circuit on the Power Supply Side>>

As illustrated in FIG. 23, the source line potential control circuit onthe power supply side of each SRAM module of three SRAM modules (SRAM1,SRAM2, SRAM3) of the semiconductor integrated circuit according toEmbodiment 9 of the present invention comprises a P-channel MOStransistor MP1 between the power supply voltage Vdd and thepower-supply-side cell array source line arvdd, and the control signalrs2 is supplied to a control gate of the P-channel MOS transistor MP1.

<<The Source Line Potential Control Circuit on the Ground Side>>

As illustrated in FIG. 23, the source line potential control circuit onthe ground side of each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment 9of the present invention, comprises a resistor RN1 and an N-channel MOStransistor MN_L1 coupled in parallel between the cell array source linearvss and the local power line vssm.

A source-to-drain path of a P-channel MOS transistor MP_M1 is coupledbetween the power supply voltage Vdd and a control gate of the N-channelMOS transistor MN_L1, and a drain-to-source path of a N-channel MOStransistor MN_M1 is coupled between a drain and the control gate of theN-channel MOS transistor MN_L1.

The control signal rsb1 is supplied to an input terminal of a CMOSinverter INV_L1, and an output signal of the CMOS inverter INV_L1 issupplied to a control gate of the P-channel MOS transistor MP_M1 and acontrol gate of the N-channel MOS transistor MN_M1.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 23, thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set at a high level, a high level, and a low level, respectively.Accordingly, the power switch PWSW is set to an on state. In the sourceline potential control circuit on the ground side, the P-channel MOStransistor MP_M1 is set to an on state, and the N-channel MOS transistorMN_L1 is set to an on state. In the source line potential controlcircuit on the power supply side, the P-channel MOS transistor MP1 isset to an on state.

Therefore, the local power line vssm is set at the ground potential Vssand the peripheral circuit power switch PESW is set to an on state;accordingly, the peripheral circuit (peripheral) is set to an activestate. Furthermore, the potential of the power-supply-side cell arraysource line arvdd is set at the power supply voltage Vdd due to the onstate of the P-channel MOS transistor MP1, the potential of theground-side cell array source line arvss is set at the ground potentialVss due to the on state of the N-channel MOS transistor MN_L1, and thecell array (cell_array) is also set to an active state; accordingly, itbecomes possible to execute write operation or read operation of theSRAM module illustrated in FIG. 23.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 23, thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set at a high level, a low level, and a low level, respectively.Accordingly, the power switch PWSW is set to an on state, the N-channelMOS transistor MN_M1 is set to an on state, and the N-channel MOStransistor MN_L1 operates as a diode.

Accordingly, the peripheral circuit power switch PESW is set to an offstate, and the peripheral circuit (peripheral) is set in a standbystate. In the source line potential control circuit on the power supplyside, the P-channel MOS transistor MP1 between the power supply voltageVdd and the power-supply-side cell array source line arvdd is controlledinto an on state. Furthermore, in the source line potential controlcircuit on the ground side, the potential of the cell array source linearvss is set at a level a little higher than the ground potential Vssdue to the diode operation of the N-channel MOS transistor MN_L1.Accordingly, current of the cell array (cell_array) is reduced to suchan extent that retained data of the cell array are not destroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 23, thecontrol signal rsb1 and the control signal rs2 are set at a low leveland a high level, respectively. Therefore, the P-channel MOS transistorMP1 of the source line potential control circuit on the power supplyside is set to an off state, and in the source line potential controlcircuit on the ground side, the N-channel MOS transistor MN_M1 is set toan on state and the N-channel MOS transistor MN_L1 is set to an offstate. Therefore, it is possible to reduce greatly the operating currentof the cell array (cell_array) of the SRAM module, by setting high avalue of resistance of the resistor RN1 of the source line potentialcontrol circuit on the ground side.

Embodiment 10

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 10>>

FIG. 24 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 10 of the present invention.

In a semiconductor integrated circuit according to Embodiment 10 of thepresent invention, although not illustrated in FIG. 24 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 10 of the present invention, a peripheralcircuit power switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22.

<<Source Line Potential Control Circuit>>

As illustrated in FIG. 24, the source line potential control circuit ofeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 10 of thepresent invention comprises an active power switch SW1, a resistor RN1,an N-channel MOS transistor MNOP1, and a deep standby switch MN2,arranged between the cell array source line arvss and the local powerline vssm. A parallel coupling body of the resistor RN1 and theN-channel MOS transistor MNOP1 is coupled with the deep standby switchMN2 in series, and the deep standby switch MN2 is coupled with the powerswitch PWSW in series.

Especially, the semiconductor integrated circuit according to Embodiment10 of the present invention illustrated in FIG. 24 comprises adifferential amplifier DA1. The potential of the cell array source linearvss of a drain of the N-channel MOS transistor MNOP1 is supplied to anoninverting input terminal (+) of the differential amplifier DA1, areference voltage Vref is supplied to an inverting input terminal (−) ofthe differential amplifier DA1, and an output signal of the differentialamplifier DA1 is supplied to a control gate of the N-channel MOStransistor MNOP1.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 24, thecontrol signal cnt, the control signal rs1, and the control signal rs2are set at a high level, a high level, and a low level, respectively.Accordingly, the power switch PWSW is set to an on state. Therefore, thelocal power line vssm is set at the ground potential Vss and theperipheral circuit power switch PESW is set to an on state; accordingly,the peripheral circuit (peripheral) is set to an active state.Furthermore, the potential of the cell array source line arvss is set atthe ground potential Vss due to the on state of the active power switchSW1, and the cell array (cell_array) is also set to an active state;accordingly, it becomes possible to execute write operation or readoperation of the SRAM module illustrated in FIG. 24.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 24, thedifferential amplifier DA1 is activated first, the control signal cnt,the control signal rs1, and the control signal rs2 are set at a highlevel, a low level, and a high level, respectively; accordingly, thepower switch PWSW is set to an on state, the peripheral circuit powerswitch PESW is set to an off state, and the peripheral circuit(peripheral) is set in a standby state. Furthermore, the active powerswitch SW1 is set to an off state, and the deep standby switch MN2 isset to an on state. Furthermore, by the activation of the differentialamplifier DA1, the control gate of the N-channel MOS transistor MNOP1 iscontrolled by the output signal of the differential amplifier DA1 sothat the potential of the cell array source line arvss of the drain ofthe N-channel MOS transistor MNOP1 may become nearly equal to thereference voltage Vref. In this way, in the source line potentialcontrol circuit, due to the operation of the differential amplifier DA1and the N-channel MOS transistor MNOP1, the potential of the cell arraysource line arvss is set at a level of the reference voltage Vref whichis a little higher than the ground potential Vss. Therefore, current ofthe cell array (cell_array) is reduced to such an extent that retaineddata of the cell array are not destroyed. The reference voltage Vref isset at a suitable voltage value, corresponding to changes of amanufacturing process, temperature, or a power supply voltage.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 24, thecontrol signal rs1 and the control signal rs2 are set to a low level anda low level, respectively, and the peripheral circuit power switch PESW,the active power switch SW1, and the deep standby switch MN2 are set toan off state. Therefore, it is possible to reduce greatly the operatingcurrent of the cell array (cell_array) of the SRAM module.

Embodiment 11

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 11>>

FIG. 25 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 11 of the present invention.

In a semiconductor integrated circuit according to Embodiment 11 of thepresent invention, although not illustrated in FIG. 25 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 11 of the present invention, a peripheralcircuit power switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22. Furthermore, a bias circuit (to be explained below) iscoupled to the source line potential control circuit.

<<Source Line Potential Control Circuit>>

As illustrated in FIG. 25, the source line potential control circuit ofeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 11 of thepresent invention comprises an active power switch SW1, an N-channel MOStransistor MNI1, and a deep standby switch MNI2, arranged between thecell array source line arvss and the local power line vssm. TheN-channel MOS transistor MNI1 and the deep standby switch MNI2 arecoupled in series, and the present series coupling body is coupled withthe active power switch SW1 in parallel.

<<Bias Circuit>>

As illustrated in FIG. 25, a bias circuit is coupled to the source linepotential control circuit of each SRAM module of three SRAM modules(SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuit accordingto Embodiment 11 of the present invention. The bias circuit comprises aresistor RN2, a P-channel MOS transistor MP_ICNT, and an N-channel MOStransistor MN_MIR, which are coupled in series between the power supplyvoltage Vdd and the local power line vssm.

In the bias circuit, a source of the P-channel MOS transistor MP_ICNT iscoupled to the power supply voltage Vdd via the resistor RN2. A controlsignal ibiase is supplied to a control gate of the P-channel MOStransistor MP_ICNT, and a drain of the P-channel MOS transistor MP_ICNTis coupled to the N-channel MOS transistor MN_MIR. By coupling a drainand a control gate of the N-channel MOS transistor MN_MIR, the diodecoupling of the N-channel MOS transistor MN_MIR is established. Thediode coupling N-channel MOS transistor MN_MIR of the bias circuit andthe N-channel MOS transistor MNI1 of the source line potential controlcircuit form a current mirror.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 25, thecontrol signal cnt and the control signal rsb1 are set at a high leveland a high level, respectively, and the power switch PWSW is set to anon state. Therefore, the local power line vssm is set at the groundpotential Vss and the peripheral circuit power switch PESW is set to anon state; accordingly the peripheral circuit (peripheral) is set to anactive state. Furthermore, the potential of the cell array source linearvss is set at the ground potential Vss due to the on state of theactive power switch SW1, and the cell array (cell_array) is also set toan active state; accordingly, it is possible to execute write operationor read operation of the SRAM module illustrated in FIG. 25.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 25, thecontrol signal ibiase is first set at a low level, and the P-channel MOStransistor MP_ICNT of the bias circuit is set to an on state. Thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set to a high level, a low level, and a high level, respectively;accordingly, the power switch PWSW is set to an on state, the peripheralcircuit power switch PESW is set to an off state, the peripheral circuit(peripheral) is set in a standby state, and the deep standby switch MNI2is set to an on state. Furthermore, the potential of the cell arraysource line arvss is set at a level a little higher than the groundpotential Vss, by the operation of the current mirror which is formed bythe diode coupling N-channel MOS transistor MN_MIR of the bias circuitand the N-channel MOS transistor MNI1 of the source line potentialcontrol circuit. Therefore, current of the cell array (cell_array) isreduced to such an extent that retained data of the cell array are notdestroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 25, thecontrol signal rsb1 and the control signal rs2 are set at a low leveland a low level, respectively; accordingly, the peripheral circuit powerswitch PESW is set to an off state, and the deep standby switch MNI2 isset to an off state. Therefore, it is possible to reduce greatly theoperating current of a cell array (cell_array) of the SRAM module.

Embodiment 12

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 12>>

FIG. 26 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 12 of the present invention.

In a semiconductor integrated circuit according to Embodiment 12 of thepresent invention, although not illustrated in FIG. 26 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 12 of the present invention, a peripheralcircuit power switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22. Furthermore, a bias circuit (to be explained below) iscoupled to the source line potential control circuit.

<<The Source Line Potential Control Circuit and the Bias Circuit>>

As illustrated in FIG. 26, the source line potential control circuit ofeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 12 of thepresent invention comprises an active power switch SW1, an N-channel MOStransistor MNI21, a deep standby switch MN2, a CMOS transfer switchPASSTR, and a CMOS inverter INV_PASS, arranged between the cell arraysource line arvss and the local power line vssm. In the source linepotential control circuit, the active power switch SW1 and the N-channelMOS transistor MNI21 are coupled in parallel between the cell arraysource line arvss and the local power line vssm. A drain-to-source pathof the deep standby switch MN2 is coupled between a control gate of theN-channel MOS transistor MNI21 and the local power line vssm. Thecontrol signal rs2 is supplied at a control gate of the deep standbyswitch MN2.

As illustrated in FIG. 26, a bias circuit is coupled to the source linepotential control circuit of each SRAM module of three SRAM modules(SRAM1, SRAM2, SRAM3) of the semiconductor integrated circuit accordingto Embodiment 12 of the present invention. The bias circuit comprises aresistor RN2, a P-channel MOS transistor MP_ICNT, and an N-channel MOStransistor MN_MIR, which are coupled in series between the power supplyvoltage Vdd and the local power line vssm.

In the bias circuit, a source of the P-channel MOS transistor MP_ICNT iscoupled to the power supply voltage Vdd via the resistor RN2. Thecontrol signal ibiase is supplied to a control gate of the P-channel MOStransistor MP_ICNT, and a drain of the P-channel MOS transistor MP_ICNTis coupled to the N-channel MOS transistor MN_MIR. By coupling a drainand a control gate of the N-channel MOS transistor MN_MIR, the diodecoupling of the N-channel MOS transistor MN_MIR is established. Thediode coupling N-channel MOS transistor MN_MIR of the bias circuit andthe N-channel MOS transistor MNI21 of the source line potential controlcircuit are coupled via a drain-to-source path of parallel-coupledP-channel MOS transistor and N-channel MOS transistor serving as theCMOS transfer switch PASSTR. The control signal rsb1 is supplied to acontrol gate of the P-channel MOS transistor of the CMOS transfer switchPASSTR and to an input terminal of the CMOS inverter INV_PASS, and anoutput signal of the CMOS inverter INV_PASS is supplied to a controlgate of the N-channel MOS transistor of the CMOS transfer switch PASSTR.In a standby state, the control signal rsb1 is set at a low level, andthe parallel-coupled P-channel MOS transistor and N-channel MOStransistor of the CMOS transfer switch PASSTR are both set to an onstate; accordingly, the diode coupling N-channel MOS transistor MN_MIRof the bias circuit and the N-channel MOS transistor MNI21 of the sourceline potential control circuit form a current mirror.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 26, thecontrol signal cnt and the control signal rsb1 are set at a high leveland a high level, respectively, and the power switch PWSW is set to anon state. Therefore, the local power line vssm is set at the groundpotential Vss, and the peripheral circuit power switch PESW is also setto an on state; accordingly, the peripheral circuit (peripheral) is setto an active state. Furthermore, the potential of the cell array sourceline arvss is set at the ground potential Vss due to the on state of theactive power switch SW1, and the cell array (cell_array) is also set toan active state; accordingly, it becomes possible to execute writeoperation or read operation of the SRAM module illustrated in FIG. 26.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 26, thecontrol signal ibiase is first set at a low level, and the P-channel MOStransistor MP_ICNT of the bias circuit is set to an on state. Thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set to a high level, a low level, and a low level, respectively;accordingly, the power switch PWSW is set to an on state, the peripheralcircuit power switch PESW is set to an off state, the peripheral circuit(peripheral) is set in a standby state, and the active power switch SW1is set to an off state. Furthermore, the potential of the cell arraysource line arvss is set at a level a little higher than the groundpotential Vss, by the operation of the current mirror which is formed bythe diode coupling N-channel MOS transistor MN_MIR of the bias circuitand the N-channel MOS transistor MNI21 of the source line potentialcontrol circuit. Therefore, current of the cell array (cell_array) isreduced to such an extent that retained data of the cell array are notdestroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 26, thecontrol signal ibiase is set at a high level, and the control signalrsb1 and the control signal rs2 are set at a low level and a high level,respectively; accordingly, the peripheral circuit power switch PESW isset to an off state, the bias circuit is set to an off state, the deepstandby switch MN2 is set to an on state, and the N-channel MOStransistor MNI21 is set to an off state. Therefore, it is possible toreduce greatly the operating current of a cell array (cell_array) of theSRAM module.

Embodiment 13

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 13>>

FIG. 27 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 13 of the present invention.

A semiconductor integrated circuit according to Embodiment 13 of thepresent invention illustrated in FIG. 27 is different from thesemiconductor integrated circuit according to Embodiment 12 of thepresent invention illustrated in FIG. 26 only in the following points.

The first different point is that the parallel coupling of the activepower switch SW1 and the N-channel MOS transistor MNI21 of the sourceline potential control circuit of the semiconductor integrated circuitaccording to Embodiment 12 of the present invention, illustrated in FIG.26, is replaced by a single N-channel MOS transistor MN23 in the sourceline potential control circuit of the semiconductor integrated circuitaccording to Embodiment 13 of the present invention, illustrated in FIG.27.

Furthermore, the second different point is that a P-channel MOStransistor MP_HOLD is added to the source line potential control circuitof the semiconductor integrated circuit according to Embodiment 13 ofthe present invention illustrated in FIG. 27, and that a source and acontrol gate and a drain of the P-channel MOS transistor MP_HOLD arecoupled to the power supply voltage Vdd, the control signal rsb1, and acontrol gate of the N-channel MOS transistor MN23, respectively.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 27, thecontrol signal cnt and the control signal rsb1 are set at a high leveland a high level, respectively, and the power switch PWSW is set to anon state. Therefore, the local power line vssm is set at the groundpotential Vss and the peripheral circuit power switch PESW is set to anon state; accordingly the peripheral circuit (peripheral) is set to anactive state. Furthermore, by the control signal rsb1 set at a highlevel, the output signal of the CMOS inverter INV_PASS is set at a lowlevel, and the P-channel MOS transistor MP_HOLD and the N-channel MOStransistor MN23 are set to an on state. As the result, the potential ofthe cell array source line arvss is set at the ground potential Vss, andthe cell array (cell_array) is also set to an active state; accordingly,it is possible to execute write operation or read operation of the SRAMmodule illustrated in FIG. 27.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 27, thecontrol signal ibiase is first set at a low level, and the P-channel MOStransistor MP_ICNT of the bias circuit is set to an on state. Thecontrol signal cnt, the control signal rsb1, and the control signal rs2are set co a high level, a low level, and a low level, respectively;accordingly, the power switch PWSW is set to an on state, the peripheralcircuit power switch PESW is set to an off state, and the peripheralcircuit (peripheral) is set in a standby state. By the control signalrsb1 set at a low level, an output signal of the CMOS inverter INV_PASSis set at a high level, the P-channel MOS transistor MP_HOLD is set toan off state, and the parallel-coupled P-channel MOS transistor andN-channel MOS transistor of the CMOS transfer switch PASSTR are both setto an on state. Therefore, the potential of the cell array source linearvss is set at a level a little higher than the ground potential Vss,by the operation of the current mirror which is formed by the diodecoupling N-channel MOS transistor MN_MIR of the bias circuit and theN-channel MOS transistor MNI23 of the source line potential controlcircuit. Therefore, current of the cell array (cell_array) is reduced tosuch an extent that retained data of the cell array are not destroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 27, thecontrol signal ibiase is set at a high level, the control signal rsb1and the control signal rs2 are set at a low level and a high level,respectively; accordingly, the peripheral circuit power switch PESW isset to an off state, the bias circuit is set to an off state, the deepstandby switch MN2 is set to an on state, and the N-channel MOStransistor MNI23 is set to an off state. Therefore, it is possible toreduce greatly the operating current of a cell array (cell_array) of theSRAM module.

Embodiment 14

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 14>>

FIG. 28 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 14 of the present invention.

A semiconductor integrated circuit according to Embodiment 14 of thepresent invention illustrated in FIG. 28 is different from thesemiconductor integrated circuit according to Embodiment 13 of thepresent invention illustrated in FIG. 27 only in the following point.

That is, the difference is that a voltage monitoring circuit(voltage_monitor) and a voltage divider circuit (Rdd, Rref, Rss) areadded in a source line potential control circuit of the semiconductorintegrated circuit according to Embodiment 14 of the present inventionillustrated in FIG. 28.

Three voltage dividing resistors Rdd, Rref, and Rss of the voltagedivider circuit are coupled in series between the power supply voltageVdd and the local power line vssm, and the potential difference acrossthe middle voltage dividing resistor Rref is supplied to one differenceinput terminal of the voltage monitoring circuit (voltage_monitor). Thepotential difference between the power supply voltage Vdd of the cellarray (cell_array) and the cell array source line arvss is supplied toanother difference input terminal of the voltage monitoring circuit(voltage_monitor).

Therefore, the voltage monitoring circuit (voltage_monitor) in a standbystate compares the potential difference between the power supply voltageVdd of the cell array (cell_array) and the cell array source line arvsswith the potential difference of the middle voltage dividing resistorRref, and controls a voltage level of the control signal ibiase suppliedto the control gate of the P-channel MOS transistor MP_ICNT of the biascircuit, so that both the potential differences agree with each other.That is, the output control signal ibiase generated from a comparisonoutput terminal (out) of the voltage monitoring circuit(voltage_monitor) is supplied to a control gate of the P-channel MOStransistor MP_ICNT of the bias circuit.

Furthermore, the voltage monitoring circuit (voltage_monitor) can alsodetect a short-circuit state between the power supply voltage Vdd andthe cell array source line arvss of the cell array (cell_array). In theshort-circuit state, the potential difference between the power supplyvoltage Vdd and the cell array source line arvss of the cell array(cell_array) falls more markedly than the potential difference of themiddle voltage dividing resistor Rref. A detection result of theshort-circuit state can be generated from another output terminal Voutof the voltage monitoring circuit (voltage_monitor).

Embodiment 15

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 15>>

FIG. 29 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 15 of the present invention.

A semiconductor integrated circuit according to Embodiment 15 of thepresent invention illustrated in FIG. 29 is different from thesemiconductor integrated circuit according to Embodiment 14 of thepresent invention illustrated in FIG. 28 only in the following point.

That is, the difference is that, in a source line potential controlcircuit of the semiconductor integrated circuit according to Embodiment15 of the present invention illustrated in FIG. 29, the bottom voltagedividing resistor Rss of the voltage divider circuit of the source linepotential control circuit of the semiconductor integrated circuitaccording to Embodiment 14 of the present invention illustrated in FIG.28 is replaced by an N-channel MOS transistor SW_REF and a CMOS inverterINV_REF.

That is, in the source line potential control circuit of thesemiconductor integrated circuit according to Embodiment 15 of thepresent invention illustrated in FIG. 29, a drain-to-source path of theN-channel MOS transistor SW_REF is coupled between the middle voltagedividing resistor Rref of the voltage divider circuit and the localpower line vssm. A control gate of the N-channel MOS transistor SW_REFis coupled to an output terminal of the CMOS inverter INV_REF, and thecontrol signal rsb1 is supplied to the input terminal of the CMOSinverter INV_REF.

Therefore, in an active state of the SRAM module illustrated in FIG. 29,the control signal rsb1 is set at a high level, and the N-channel MOStransistor SW_REF is set to an off state; accordingly, the consumptioncurrent of the voltage divider circuit is reduced. In a standby stateand a deep standby state, the control signal rsb1 is set at a low level,and the N-channel MOS transistor SW_REF is set to an on state;accordingly, the operating current is supplied to the middle voltagedividing resistor Rref of the voltage divider circuit.

Embodiment 16

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 16>>

FIG. 30 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 16 of the present invention.

A semiconductor integrated circuit according to Embodiment 16 of thepresent invention illustrated in FIG. 30 is different from thesemiconductor integrated circuit according to Embodiment 11 of thepresent invention illustrated in FIG. 25 only in the following point.

That is, the difference is that, in the semiconductor integrated circuitaccording to Embodiment 16 of the present invention illustrated in FIG.30, the bias circuit comprising the resistor RN2, the P-channel MOStransistor MP_ICNT, and the N-channel MOS transistor MN_MIR, which arecoupled in series between the power supply voltage Vdd and the localpower line vssm, is shared by plural source line potential controlcircuits of plural SRAM modules Module1 and Module2. The plural SRAMmodules Module1 and Module2 may be the first and the second SRAM module(SRAM1, SRAM2), the second and the third SRAM module (SRAM2, SRAM3), orthe first and the third SRAM module (SRAM1, SRAM3).

In the semiconductor integrated circuit according to Embodiment 16 ofthe present invention illustrated in FIG. 30, an N-channel MOStransistor MNI1 and a deep standby switch MNI2 are coupled in seriesbetween the local power line vssm and plural cell array source linearvss1 and arvss2 of plural cell arrays (cell_array) of the plural SRAMmodules Module1 and Module2. The series-coupled N-channel MOS transistorMNI1 and deep standby switch MNI2 are shared by the plural source linepotential control circuits of the plural cell arrays (cell_array) of theplural SRAM modules Module1 and Module2. A control gate of the sharedN-channel MOS transistor MNI1 is coupled to the N-channel MOS transistorMN_MIR of the bias circuit in the form of a current mirror. In this way,in the semiconductor integrated circuit according to Embodiment 16 ofthe present invention illustrated in FIG. 30, the bias circuit is sharedby the plural SRAM modules. Therefore, it is possible to reduce thenumber of bias circuits and the bias current.

Embodiment 17

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 17>>

FIG. 31 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 17 of the present invention.

A semiconductor integrated circuit according to Embodiment 17 of thepresent invention illustrated in FIG. 31 is different from thesemiconductor integrated circuit according to Embodiment 16 of thepresent invention illustrated in FIG. 30 only in the following points.

The first difference is that, in a source line potential control circuitof the semiconductor integrated circuit according to Embodiment 17 ofthe present invention illustrated in FIG. 31, the deep standby switchMNI2 of the source line potential control circuit illustrated in FIG. 30is deleted and the source of the N-channel MOS transistor MNI1 isdirectly coupled to the local power line vssm.

The second difference is that, in the semiconductor integrated circuitaccording to Embodiment 17 of the present invention illustrated in FIG.31, a drain-to-source path of a first deep standby switch MNS_M1 iscoupled between the cell array source line arvss1 of the cell array(cell_array) of the first SRAM module Module1 and the drain of theN-channel MOS transistor MNI1, and that a drain-to-source path of asecond deep standby switch MNS_M2 is coupled between the cell arraysource line arvss2 of the cell array (cell_array) of the second SRAMmodule Module2 and the drain of the N-channel MOS transistor MNI1.

In a deep standby state of the first SRAM module Module1, a controlsignal rsb2 is set at a low level, and the first deep standby switchMNS_M1 coupled between the cell array source line arvss1 of the cellarray (cell_array) of the first SRAM module Module1 and the drain of theN-channel MOS transistor MNI1 is set to an off state. In a deep standbystate of the second SRAM module Module2, a control signal rsb3 is set ata low level, and the second deep standby switch MNS_M2 coupled betweenthe cell array source line arvss2 of the cell array (cell_array) of thesecond SRAM module Module2 and the drain of the N-channel MOS transistorMNI1 is set to an off state.

Embodiment 18

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 18>>

FIG. 32 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 18 of the present invention.

A semiconductor integrated circuit according to Embodiment 18 of thepresent invention illustrated in FIG. 32 is different from thesemiconductor integrated circuit according to Embodiment 3 of thepresent invention illustrated in FIG. 14 only in the following points.

The first difference is that the deep standby switch which comprises aP-channel MOS transistor coupled between the power supply voltage Vddand the cell array (cell_array) in FIG. 14 comprises plural P-channelMOS transistors MPSW1, - - - , MPSWm in FIG. 32.

The second difference is that the plural P-channel MOS transistorsMPSW1, - - - , MPSWm of the deep standby switch are respectively coupledto plural cell array source lines arvdd1, - - - , arvddm, which arearranged in the column direction (in the direction of a complementarybit-line pair) of the cell array (cell_array). Each cell array sourceline of the plural cell array source lines arvdd1, - - - , arvddm iscoupled with each of plural memory cells (MC) arranged in the columndirection (in the direction of the complementary bit-line pair) of thecell array (cell_array).

The third difference is that plural control signals rspb1, - - - , rspbmare supplied to the control gates of the plural P-channel MOStransistors MPSW1, - - - , MPSWm.

The standby current of all the memory cells (MC) included in one cellarray (cell_array) can be restricted by one resistor RN1 and one diodecoupling MOS transistor MN1 of the source line potential controlcircuit.

In a deep standby state, by a control signal set at a high level amongthe plural control signals rspb1, - - - , rspbm, it is possible to cutoff the current of a memory cell (MC) of a cell array source line whichis coupled to a P-channel MOS transistor in an off state among theplural P-channel MOS transistors MPSW1, - - - , MPSWm.

Embodiment 19

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 19>>

FIG. 33 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 19 of the present invention.

A semiconductor integrated circuit according to Embodiment 19 of thepresent invention illustrated in FIG. 33 is different from thesemiconductor integrated circuit according to Embodiment 18 of thepresent invention illustrated in FIG. 32 only in the following point.

That is, the difference is that each SRAM module of the semiconductorintegrated circuit according to Embodiment 19 of the present inventionillustrated in FIG. 33 adopts a two-column multiplex system, as is thecase with each SRAM module of the semiconductor integrated circuitaccording to Embodiment 1 of the present invention illustrated in FIG.7. Therefore, in each SRAM module illustrated in FIG. 33, two pairs ofcomplementary bit-line pairs are coupled to each selector(SELECTOR[1], - - - , SELECTOR[n]).

A drain-to-source path of a first P-channel MOS transistor MPSW1 of thedeep standby switch, to the control gate of which the first controlsignal rspb1 is supplied, is coupled between the power supply voltageVdd and the first cell array source line arvdd1 of a memory cell (MC)which is coupled to the left-hand first complementary bit-line paircoupled to each selector (SELECTOR[1], - - - , SELECTOR[n]). When thefirst control signal rspb1 is set at a low level, the first P-channelMOS transistor MPSW1 is set to an on state, and when the first controlsignal rspb1 is set at a high level, the first P-channel MOS transistorMPSW1 is set to an off state. In addition, a drain-to-source path of asecond P-channel MOS transistor MPSW2 of the deep standby switch, to thecontrol gate of which the second control signal rspb2 is supplied, iscoupled between the power supply voltage Vdd and the second cell arraysource line arvdd2 of a memory cell (MC) which is coupled to theright-hand second complementary bit-line pair coupled to each selector(SELECTOR[1], - - - , SELECTOR[n]). When the second control signal rspb2is set at a low level, the second P-channel MOS transistor MPSW2 is setto an on state, and when the second control signal rspb2 is set at ahigh level, the second P-channel MOS transistor MPSW2 is set to an offstate.

However, even in Embodiment 19 of the present invention illustrated inFIG. 33, as is the case with Embodiment 18 of the present inventionillustrated in FIG. 32, the standby current of all the memory cells (MC)included in one cell array (cell_array) can be restricted by oneresistor RN1 and one diode coupling MOS transistor MN1 of the sourceline potential control circuit.

Embodiment 20

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 20>>

FIG. 34 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 20 of the present invention.

In a semiconductor integrated circuit according to Embodiment 20 of thepresent invention, although not illustrated in FIG. 34 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 20 of the present invention, a peripheralcircuit power switch PESW21 is coupled between the peripheral circuit(peripheral) and the first local power line vssl21, and a source linepotential control circuit (to be explained below) is coupled between thecell array source line arvss21 of the cell array (cell_array) and thefirst local power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and asource line potential control circuit (to be explained below) is coupledbetween the cell array source line arvss22 of the cell array(cell_array) and the second local power line vssm22. Furthermore, alsoin the third SRAM module (SRAM3), a peripheral circuit power switchPESW23 is coupled between the peripheral circuit (peripheral) and thesecond local power line vssm22, and a source line potential controlcircuit (to be explained below) is coupled between the cell array sourceline arvss23 of the cell array (cell_array) and the second local powerline vssm22.

<<Source Line Potential Control Circuit>>

As illustrated in FIG. 34, the source line potential control circuit ofeach SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3) of thesemiconductor integrated circuit according to Embodiment 20 of thepresent invention comprises a first source line potential controlcircuit and a second source line potential control circuit.

The first source line potential control circuit comprises a resistorRN1, a diode coupling N-channel MOS transistor MN1, and a deep standbyswitch MN2, arranged between the cell array source line arvss and thelocal power line vssm. A parallel coupling body of the resistor RN1 andthe diode coupling N-channel MOS transistor MN1 is coupled with the deepstandby switch MN2 in series. A deep standby control signal rcut1 issupplied to a control gate of the deep standby switch MN2. In a deepstandby state, the deep standby control signal rcut1 is set at a lowlevel, and the deep standby switch MN2 is set to an off state. A P-wellof the diode coupling N-channel MOS transistor MN1 is coupled to asource.

The second source line potential control circuit comprises a resistorRN2, a diode coupling N-channel MOS transistor MN3, and a deep standbyswitch MN4, arranged between the cell array source line arvss and thelocal power line vssm. A parallel coupling body of the resistor RN2 andthe diode coupling N-channel MOS transistor MN3 is coupled with the deepstandby switch MN4 in series. A deep standby control signal rcut2 issupplied to a control gate of the deep standby switch MN4. In a deepstandby state, the deep standby control signal rcut2 is set at a lowlevel, and the deep standby switch MN4 is set to an off state. A P-wellof the diode coupling N-channel MOS transistor MN3 is coupled to thelocal power line Vssm.

Embodiment 21

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 21>>

FIG. 35 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 21 of the present invention.

In a semiconductor integrated circuit according to Embodiment 21 of thepresent invention, although not illustrated in FIG. 35 but as is thecase with the semiconductor integrated circuit according to Embodiment 2of the present invention illustrated in FIG. 11, the local power line ofthe logic circuit (logic) and the local power line of the first SRAMmodule (SRAM1) share the first local power line vssl21, and the localpower line of the second SRAM module (SRAM2) and the local power line ofthe third SRAM module (SRAM3) share the second local power line vssm22.The first power switch PWSW21 coupled between the shared first localpower line vssl21 and the ground potential Vss is shared by the logiccircuit (logic) and the first SRAM module (SRAM1). Furthermore, thesecond power switch PWSW22 and the third power switch PWSW23, which arecoupled between the shared second local power line vssm22 and the groundpotential Vss, are shared by the second SRAM module (SRAM2) and thethird SRAM module (SRAM3).

In the first SRAM module (SRAM1) of the semiconductor integrated circuitaccording to Embodiment 21 of the present invention illustrated in FIG.35, a peripheral circuit power switch PESW21 is coupled between theperipheral circuit (peripheral) and the first local power line vssl21,and an active power switch SW21 and a ground-side source line potentialcontrol circuit (to be explained below) are coupled between the cellarray source line arvss21 of the cell array (cell_array) and the firstlocal power line vssl21. Also in the second SRAM module (SRAM2), aperipheral circuit power switch PESW22 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and anactive power switch SW22 and a ground-side source line potential controlcircuit (to be explained below) are coupled between the cell arraysource line arvss22 of the cell array (cell_array) and the second localpower line vssm22. Furthermore, also in the third SRAM module (SRAM3), aperipheral circuit power switch PESW23 is coupled between the peripheralcircuit (peripheral) and the second local power line vssm22, and anactive power switch SW23 and a ground-side source line potential controlcircuit (to be explained below) are coupled between the cell arraysource line arvss23 of the cell array (cell_array) and the second localpower line vssm22.

Furthermore, in the first SRAM module (SRAM1) of the semiconductorintegrated circuit according to Embodiment 21 of the present inventionillustrated in FIG. 35, an active power switch SWP21 and apower-supply-side source line potential control circuit (to be explainedbelow) are coupled between the cell array source line arvdd21 of thecell array (cell_array) and the power supply voltage Vdd. Also in thesecond SRAM module (SRAM2), an active power switch SWP22 and apower-supply-side source line potential control circuit (to be explainedbelow) are coupled between the cell array source line arvdd22 of thecell array (cell_array) and the power supply voltage Vdd. Furthermore,also in the third SRAM module (SRAM3), an active power switch SWP23 anda power-supply-side source line potential control circuit (to beexplained below) are coupled between the cell array source line arvdd23of the cell array (cell_array) and the power supply voltage Vdd.

<<The Source Line Potential Control Circuit on the Ground Side>>

As illustrated in FIG. 35, the source line potential control circuit onthe ground side of each SRAM module of three SRAM modules (SRAM1, SRAM2,SRAM3) of the semiconductor integrated circuit according to Embodiment21 of the present invention comprises a resistor RN1, a diode couplingN-channel MOS transistor MN1, and a deep standby switch MN2, arrangedbetween the cell array source line arvss and the local power line vssm.A parallel coupling body of the resistor RN1 and the diode couplingN-channel MOS transistor MN1 is coupled with the deep standby switch MN2in series. A control signal rs2 is supplied to a control gate of thedeep standby switch MN2. In a deep standby state, the control signal rs2is set at a low level, and the deep standby switch MN2 is set to an offstate. A P-well of the diode coupling N-channel MOS transistor MN1 iscoupled to the local power line vssm.

<<A Source Line Potential Control Circuit on the Power Supply Side>>

As illustrated in FIG. 35, the source line potential control circuit onthe power supply side of each SRAM module of three SRAM modules (SRAM1,SRAM2, SRAM3) of the semiconductor integrated circuit according toEmbodiment 21 of the present invention comprises a resistor RP1, a diodecoupling P-channel MOS transistor MP1, and a deep standby switch MP2,arranged between the cell array source line arvdd and the power supplyvoltage Vdd. A parallel coupling body of the resistor RP1 and the diodecoupling P-channel MOS transistor MP1 is coupled with the deep standbyswitch MP2 in series. A control signal rsp2 is supplied to a controlgate of the deep standby switch MP2. In a deep standby state, thecontrol signal rsp2 is set at a high level, and the deep standby switchMP2 is set to an off state. An N-well of the diode coupling P-channelMOS transistor MP1 is coupled to the power supply voltage Vdd.

<<Active State>>

In an active state of the SRAM module illustrated in FIG. 35, thecontrol signal cnt, the control signal rs1, the control signal rs2, thecontrol signal rsp1, and the control signal rsp2 are set at a highlevel, a high level, a high level, a low level, and a low level,respectively.

Therefore, the power switch PWSW, the peripheral circuit power switchPESW21, and the active power switches SW1 and SWP1 are set to an onstate, the deep standby switch MN2 of the source line potential controlcircuit on the ground side is set to an on state, and the deep standbyswitch MP2 of the source line potential control circuit on the powersupply side is set to an on state.

Therefore, the local power line vssm is set at the ground potential Vssand the peripheral circuit power switch PESW is set to an on state;accordingly, the peripheral circuit (peripheral) is set to an activestate. Furthermore, the potential of the power-source-side cell arraysource line arvdd is set at the power supply voltage Vdd, the potentialof the ground-side cell array source line arvss is set at the groundpotential Vss, and the cell array (cell_array) is also set to an activestate; accordingly, it is possible to execute write operation or readoperation of the SRAM module illustrated in FIG. 35.

<<Standby State>>

In a standby state of the SRAM module illustrated in FIG. 35, thecontrol signal cnt, the control signal rs1, the control signal rs2, thecontrol signal rsp1, and the control signal rsp2 are set at a highlevel, a low level, a high level, a high level, and a low level,respectively.

Therefore, the power switch PWSW, the peripheral circuit power switchPESW21, and the active power switches SW1 and SWP1 are set to an offstate; accordingly, the peripheral circuit (peripheral) is set in astandby state. The deep standby switch MN2 of the source line potentialcontrol circuit on the ground side is set to an on state, and the deepstandby switch MP2 of the source line potential control circuit of thepower supply side is set to an on state. Furthermore, in the source linepotential control circuit on the ground side, the potential of the cellarray source line arvss is set at a level a little higher than theground potential Vss due to the diode operation of the N-channel MOStransistor MN1. In the source line potential control circuit on thepower supply side, the potential of the cell array source line arvdd isset at a level a little lower than the power supply voltage Vdd due tothe diode operation of the P-channel MOS transistor MP1. Accordingly,current of the cell array (cell_array) is reduced to such an extent thatretained data of the cell array are not destroyed.

<<Deep Standby State>>

In a deep standby state of the SRAM module illustrated in FIG. 35, thecontrol signal cnt, the control signal rs1, the control signal rs2, thecontrol signal rsp1, and the control signal rsp2 are set at a highlevel, a low level, a low level, a high level, and a high level,respectively.

Therefore, the power switch PWSW, the peripheral circuit power switchPESW21, and the active power switches SW1 and SWP1 are set to an offstate. The deep standby switch MN2 of the source line potential controlcircuit on the ground side is set to an off state, and the deep standbyswitch MP2 of the source line potential control circuit on the powersupply side is set to an off state. As the result, it is possible toreduce greatly the operating current of a cell array (cell_array) of theSRAM module.

Embodiment 22

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 22>>

FIG. 36 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 22 of the present invention.

A semiconductor integrated circuit according to Embodiment 22 of thepresent invention illustrated in FIG. 36 is different from thesemiconductor integrated circuit according to Embodiment 20 of thepresent invention illustrated in FIG. 34 only in the following point.

That is, the difference is that, in each SRAM module of thesemiconductor integrated circuit according to Embodiment 20 of thepresent invention illustrated in FIG. 36, the resistor RN2, the diodecoupling N-channel MOS transistor MN3, and the deep standby switch MN4are omitted from the second source line potential control circuitcoupled between the local power line vssm and the cell array source linearvss of each SRAM module of the semiconductor integrated circuitaccording to Embodiment 20 of the present invention illustrated in FIG.34.

Embodiment 23

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 23>>

FIG. 37 illustrates a configuration of each SRAM module of three SRAMmodules (SRAM1, SRAM2, SRAM3) included in a semiconductor integratedcircuit according to Embodiment 23 of the present invention.

A semiconductor integrated circuit according to Embodiment 23 of thepresent invention illustrated in FIG. 37 is different from thesemiconductor integrated circuit according to Embodiment 22 of thepresent invention illustrated in FIG. 36 only in the following point.

That is, the difference is that the P-well of the diode couplingN-channel MOS transistor MN1 of the source line potential controlcircuit of each SRAM module of three SRAM modules (SRAM1, SRAM2, SRAM3)included in the semiconductor integrated circuit according to Embodiment23 of the present invention illustrated in FIG. 37, is coupled to thelocal power line vssm instead of the source.

Embodiment 24

<<A Configuration of a Semiconductor Integrated Circuit According toEmbodiment 24>>

FIG. 1 illustrates an example of a configuration of a semiconductorintegrated circuit according to Embodiment 24 of the present inventionwhich comprises three built-in SRAM modules (SRAM1, SRAM2, SRAM3)according to one of Embodiment 1 through Embodiment 23 of the presentinvention.

A semiconductor chip of the semiconductor integrated circuit illustratedin FIG. 1 comprises a first central processing unit (CPU1) and a secondcentral processing unit (CPU2) which form a multiple-processor, and animage processing unit (Video) and an audio processing unit (Audio) formoving image encoding/decoding of MPEG2 (MPEG: Moving Picture ExpertGroup).

Each unit of the first central processing unit (CPU1), the secondcentral processing unit (CPU2), the image processing unit (Video), andthe audio processing unit (Audio) comprises three built-in SRAM modules(SRAM1, SRAM2, SRAM3) according to one of Embodiment 1 throughEmbodiment 23 of the present invention described above. In each unit,the amount of saved data in a deep standby state of the built-in SRAMmodules (SRAM1, SRAM2, SRAM3) of each unit changes depending on theoperating states of each unit.

According to the semiconductor integrated circuit according toEmbodiment 24 of the present invention illustrated in FIG. 1, it becomespossible to respond suitably to such a change of the amount of saveddata in a deep standby state.

As described above, the invention accomplished by the present inventorshas been concretely explained based on various embodiments. However, itcannot be overemphasized that the present invention is not restricted tothe embodiments, and it can be changed variously in the range which doesnot deviate from the gist.

For example, in the semiconductor integrated circuit according toEmbodiment 2 of the present invention illustrated in FIG. 11, orEmbodiment 4 of the present invention illustrated in FIG. 18, it ispossible to omit either one of the second power switch PWSW22 or thethird power switch PWSW23, which are coupled between the groundpotential Vss and the second local power line vssm22 shared by thesecond SRAM module (SRAM2) and the third SRAM module (SRAM3).

Furthermore, in addition to the semiconductor integrated circuitemployed for moving image encoding/decoding illustrated in FIG. 1, thepresent invention can be applied to various system on a chips (SoC), forexample, which are usable to various applications, such as pluralcentral processing units which form a multiple-processor for enginecontrol of a car, a micro controller which has an A/D converter or a D/Aconverter built in, and others.

What is claimed is:
 1. A semiconductor device, comprising: a memory cellarray having a plurality of memory cells; a first power line coupled tothe memory cell array; a second power line coupled to a first potential;a third power line coupled to a second potential; a first N-channeltransistor which has a first electrode coupled to the first power line,a second electrode coupled to the second power line and a first controlgate, the first N-channel transistor controlling conductivity betweenthe first electrode and the second electrode; a second N-channeltransistor which has a third electrode coupled to the first power line,a fourth electrode coupled to the first control gate and a secondcontrol gate, the second N-channel transistor controlling conductivitybetween the third electrode and the fourth electrode; a third N-channeltransistor which has a fifth electrode coupled to the second power line,a sixth electrode coupled to the control gate of the first N-channeltransistor and a third control gate, the third N-channel transistorcontrolling conductivity between the fifth electrode and the sixthelectrode; a P-channel transistor which has a seventh electrode coupledto the third power line, an eighth electrode coupled to the control gateof the first N-channel transistor and a sixth control gate, theP-channel transistor controlling conductivity between the seventhelectrode and the eighth electrode; and a resistor coupled in betweenthe first power line and the second power line, wherein each of theplurality of memory cells comprising a fourth N-channel transistorhaving a first source electrode coupled to the first power line, a firstdrain electrode and a fourth control gate, and a fifth N-channeltransistor having a second source electrode coupled to the first powerline, a second drain electrode coupled to the fourth control gate and afifth control gate coupled to the first drain electrode, wherein thefirst, the second, the third and sixth control gates receive signalswhich control on and off states of each of the transistors based on afirst control signal and a second control signal.
 2. The semiconductordevice according to claim 1, wherein the first control gate iselectrically connected to the sixth electrode of the third N-channeltransistor, regardless of whether the second N-channel transistor is inan on-state or in an off-state.
 3. The semiconductor device according toclaim 2, wherein the first control gate is electrically connected to thesixth electrode of the third N-channel transistor, regardless of whetherthe P-channel transistor is in an on-state or in an off-state.
 4. Thesemiconductor device according to claim 1, wherein the first controlgate is electrically connected to the sixth electrode of the thirdN-channel transistor, regardless of whether the P-channel transistor isin an on-state or in an off-state.
 5. The semiconductor device accordingto claim 1, wherein by setting the third N-channel transistor intoon-state, the semiconductor device is capable to be set in a firstoperating state in which the first N-channel transistor is in anoff-state.
 6. The semiconductor device according to claim 5, wherein bysetting the third N-channel transistor into off-state and setting thesecond N-channel transistor into on-state, the semiconductor device iscapable to be set in a second operating state in which the control gateand the first electrode of the first N-channel transistor areelectrically connected.
 7. The semiconductor device according to claim6, wherein by setting the third N-channel transistor into off-state andsetting the P-channel transistor into on-state, the semiconductor deviceis capable to be set in a third operating state in which the firstN-channel transistor is in an on-state.
 8. A semiconductor device,comprising: a memory cell array having a plurality of memory cells; afirst power line coupled to the memory cell array; a second power linecoupled to a first potential; a third power line coupled to a secondpotential; a first N-channel transistor which has a first electrodecoupled to the first power line, a second electrode coupled to thesecond power line and a first control gate, the first N-channeltransistor controlling conductivity between the first electrode and thesecond electrode; a second N-channel transistor which has a thirdelectrode coupled to the first power line, a fourth electrode and asecond control gate, the second N-channel transistor controllingconductivity between the third electrode and the fourth electrode; athird N-channel transistor which has a fifth electrode coupled to thesecond power line, a sixth electrode coupled to the first control gateand a third control gate, the third N-channel transistor controllingconductivity between the fifth electrode and the sixth electrode; and aP-channel transistor which has a seventh electrode coupled to the thirdpower line, an eighth electrode coupled to the first control gate and asixth control gate, the P-channel transistor controlling conductivitybetween the seventh electrode and the eighth electrode, wherein each ofthe plurality of memory cells comprising a fourth N-channel transistorhaving a first source electrode coupled to the first power line, a firstdrain electrode and a fourth control gate, and a fifth N-channeltransistor having a second source electrode coupled to the first powerline, a second drain electrode coupled to the fourth control gate and afifth control gate coupled to the first drain electrode, wherein thefirst control gate is electrically connected to the sixth electrode,without passing through any transistors having an electrode coupled tothe control gate of the P-channel transistor.
 9. A semiconductor device,comprising: a memory cell array having a plurality of memory cells; afirst power line coupled to the memory cell array; a second power linecoupled to a first potential; a third power line coupled to a secondpotential; a first N-channel transistor which has a first electrodecoupled to the first power line, a second electrode coupled to thesecond power line and a first control gate, the first N-channeltransistor controlling conductivity between the first electrode and thesecond electrode; a second N-channel transistor which has a thirdelectrode coupled to the first power line, a fourth electrode coupled tothe first control gate and a third control gate controlled on the basisof a control signal, the second N-channel transistor controllingconductivity between the third electrode and the fourth electrode; athird N-channel transistor which has a fifth electrode coupled to thesecond power line, a sixth electrode coupled to the first control gateand a third control gate, the third N-channel transistor controllingconductivity between the fifth electrode and the sixth electrode; and aP-channel transistor which has a seventh electrode coupled to the thirdpower line, an eighth electrode coupled to the first control gate and asixth control gate controlled on the basis of the control signal, andwhich controls conductivity between the seventh electrode and the eighthelectrode, wherein each of the plurality of memory cells comprising afourth N-channel transistor having a first source electrode coupled tothe first power line, a first drain electrode and a fourth control gate,and a fifth N-channel transistor having a second source electrodecoupled to the first power line, a drain electrode coupled to the fourthcontrol gate and a fifth control gate coupled to the first drainelectrode, wherein the first control gate is electrically connected tothe sixth electrode, without passing through the second N-channeltransistor.